diff --git a/CHANGES.md b/CHANGES.md
index 77f7aec7fbe..4b5a1bfe1e3 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -25,6 +25,9 @@ next
 
 - Scan the file system lazily (#732, fixes #718 and #228, @diml)
 
+- Add support for setting the default ocaml flags and for build
+  profiles (#419, @diml)
+
 1.0+beta20 (10/04/2018)
 -----------------------
 
diff --git a/bin/main.ml b/bin/main.ml
index c822c3b7fa8..f77b0bf208d 100644
--- a/bin/main.ml
+++ b/bin/main.ml
@@ -11,7 +11,7 @@ type common =
   { debug_dep_path        : bool
   ; debug_findlib         : bool
   ; debug_backtraces      : bool
-  ; dev_mode              : bool
+  ; profile               : string option
   ; workspace_file        : string option
   ; root                  : string
   ; target_prefix         : string
@@ -33,7 +33,6 @@ let set_common c ~targets =
   Clflags.debug_dep_path := c.debug_dep_path;
   Clflags.debug_findlib := c.debug_findlib;
   Clflags.debug_backtraces := c.debug_backtraces;
-  Clflags.dev_mode := c.dev_mode;
   Clflags.capture_outputs := c.capture_outputs;
   if c.root <> Filename.current_dir_name then
     Sys.chdir c.root;
@@ -80,6 +79,7 @@ module Main = struct
       ?only_packages:common.only_packages
       ?external_lib_deps_mode
       ?x:common.x
+      ?profile:common.profile
       ~ignore_promoted_rules:common.ignore_promoted_rules
       ~capture_outputs:common.capture_outputs
       ()
@@ -211,7 +211,6 @@ let common =
         debug_dep_path
         debug_findlib
         debug_backtraces
-        dev_mode
         no_buffer
         workspace_file
         diff_command
@@ -221,6 +220,7 @@ let common =
          only_packages,
          ignore_promoted_rules,
          config_file,
+         profile,
          orig)
         x
         display
@@ -236,7 +236,7 @@ let common =
     in
     let orig_args =
       List.concat
-        [ if dev_mode then ["--dev"] else []
+        [ dump_opt "--profile" profile
         ; dump_opt "--workspace" workspace_file
         ; orig
         ]
@@ -264,7 +264,7 @@ let common =
     { debug_dep_path
     ; debug_findlib
     ; debug_backtraces
-    ; dev_mode
+    ; profile
     ; capture_outputs = not no_buffer
     ; workspace_file
     ; root
@@ -334,7 +334,27 @@ let common =
     Arg.(value
          & flag
          & info ["dev"] ~docs
-             ~doc:{|Use stricter compilation flags by default.|})
+             ~doc:{|Same as $(b,--profile dev)|})
+  in
+  let profile =
+    Arg.(value
+         & opt (some string) None
+         & info ["profile"] ~docs
+             ~doc:{|Select the build profile, for instance $(b,dev) or $(b,release).
+                    The default is $(b,default).|})
+  in
+  let profile =
+    let merge dev profile =
+      match dev, profile with
+      | false, x    -> `Ok x
+      | true , None -> `Ok (Some "dev")
+      | true , Some _ ->
+        `Error (true,
+                "Cannot use --dev and --profile simultaneously")
+    in
+    Term.(ret (const merge
+               $ dev
+               $ profile))
   in
   let display =
     let verbose =
@@ -440,34 +460,39 @@ let common =
            & opt (some string) None
            & info ["p"; for_release] ~docs ~docv:"PACKAGES"
                ~doc:{|Shorthand for $(b,--root . --only-packages PACKAGE
-                      --promote ignore --no-config).
+                      --promote ignore --no-config --profile release).
                       You must use this option in your $(i,<package>.opam) files, in order
                       to build only what's necessary when your project contains multiple
                       packages as well as getting reproducible builds.|})
     in
     let merge root only_packages ignore_promoted_rules
-          (config_file_opt, config_file) release =
+          (config_file_opt, config_file) profile release =
       let fail opt = incompatible ("-p/--" ^ for_release) opt in
-      match release, root, only_packages, ignore_promoted_rules, config_file_opt with
-      | Some _, Some _, _, _, _      -> fail "--root"
-      | Some _, _, Some _, _, _      -> fail "--only-packages"
-      | Some _, _, _, true  , _      -> fail "--ignore-promoted-rules"
-      | Some _, _, _, _     , Some s -> fail s
-      | Some pkgs, None, None, false, None ->
+      match release, root, only_packages, ignore_promoted_rules,
+            profile, config_file_opt with
+      | Some _, Some _, _, _, _, _ -> fail "--root"
+      | Some _, _, Some _, _, _, _ -> fail "--only-packages"
+      | Some _, _, _, true  , _, _ -> fail "--ignore-promoted-rules"
+      | Some _, _, _, _, Some _, _ -> fail "--profile"
+      | Some _, _, _, _, _, Some s -> fail s
+      | Some pkgs, None, None, false, None, None ->
         `Ok (Some ".",
              Some pkgs,
              true,
              No_config,
+             Some "release",
              ["-p"; pkgs]
             )
-      | None, _, _, _, _ ->
+      | None, _, _, _, _, _ ->
         `Ok (root,
              only_packages,
              ignore_promoted_rules,
              config_file,
+             profile,
              List.concat
                [ dump_opt "--root" root
                ; dump_opt "--only-packages" only_packages
+               ; dump_opt "--profile" profile
                ; if ignore_promoted_rules then
                    ["--ignore-promoted-rules"]
                  else
@@ -484,6 +509,7 @@ let common =
                $ only_packages
                $ ignore_promoted_rules
                $ config_file
+               $ profile
                $ frop))
   in
   let x =
@@ -503,7 +529,6 @@ let common =
         $ ddep_path
         $ dfindlib
         $ dbacktraces
-        $ dev
         $ no_buffer
         $ workspace_file
         $ diff_command
@@ -520,7 +545,11 @@ let installed_libraries =
     set_common common ~targets:[];
     let env = Main.setup_env ~capture_outputs:common.capture_outputs in
     Scheduler.go ~log:(Log.create common) ~common
-      (Context.create (Default [Native]) ~env >>= fun ctxs ->
+      (Context.create
+         (Default { targets = [Native]
+                  ; profile = "default" })
+         ~env
+       >>= fun ctxs ->
        let ctx = List.hd ctxs in
        let findlib = ctx.findlib in
        if na then begin
@@ -783,8 +812,8 @@ let external_lib_deps =
            (Build_system.all_lib_deps_by_context setup.build_system ~request)
            ~f:(fun context_name lib_deps acc ->
              let internals =
-               Jbuild.Stanzas.lib_names
-                 (match String.Map.find setup.Main.stanzas context_name with
+               Super_context.internal_lib_names
+                 (match String.Map.find setup.Main.scontexts context_name with
                   | None -> assert false
                   | Some x -> x)
              in
@@ -1297,6 +1326,59 @@ let promote =
           $ common)
   , Term.info "promote" ~doc ~man )
 
+let printenv =
+  let doc = "Print the environment of a directory" in
+  let man =
+    [ `S "DESCRIPTION"
+    ; `P {|$(b,dune printenv DIR) prints the environment of a directory|}
+    ; `Blocks help_secs
+    ] in
+  let go common dir =
+    set_common common ~targets:[];
+    let log = Log.create common in
+    Scheduler.go ~log ~common (
+      Main.setup ~log common >>= fun setup ->
+      let dir = Path.of_string dir in
+      check_path setup.contexts dir;
+      let request =
+        let dump sctx ~dir =
+          let open Build.O in
+          Super_context.dump_env sctx ~dir
+          >>^ fun env ->
+          ((Super_context.context sctx).name, env)
+        in
+        Build.all (
+          match Path.extract_build_context dir with
+          | Some (ctx, _) ->
+            let sctx =
+              String_map.find setup.scontexts ctx |> Option.value_exn
+            in
+            [dump sctx ~dir]
+          | None ->
+            String_map.values setup.scontexts
+            |> List.map ~f:(fun sctx ->
+              let dir =
+                Path.append (Super_context.context sctx).build_dir dir
+              in
+              dump sctx ~dir)
+        )
+      in
+      Build_system.do_build setup.build_system ~request
+      >>| fun l ->
+      let pp ppf = Format.fprintf ppf "@[<v1>(@,@[<v>%a@]@]@,)" (Format.pp_print_list Sexp.pp) in
+      match l with
+      | [(_, env)] ->
+        Format.printf "%a@." pp env
+      | l ->
+        List.iter l ~f:(fun (name, env) ->
+          Format.printf "@[<v2>Environment for context %s:@,%a@]@." name pp env)
+    )
+  in
+  ( Term.(const go
+          $ common
+          $ Arg.(value & pos 0 dir "" & info [] ~docv:"PATH"))
+  , Term.info "printenv" ~doc ~man )
+
 module Help = struct
   let config =
     ("dune-config", 5, "", "Dune", "Dune manual"),
@@ -1412,6 +1494,7 @@ let all =
   ; rules
   ; utop
   ; promote
+  ; printenv
   ; Help.help
   ]
 
diff --git a/doc/dune.inc b/doc/dune.inc
index f915ebab95d..2effc9cd2cb 100644
--- a/doc/dune.inc
+++ b/doc/dune.inc
@@ -62,6 +62,15 @@
  ((section man)
   (files (dune-installed-libraries.1))))
 
+(rule
+ ((targets (dune-printenv.1))
+  (action  (with-stdout-to ${@}
+            (run dune printenv --help=groff)))))
+
+(install
+ ((section man)
+  (files (dune-printenv.1))))
+
 (rule
  ((targets (dune-promote.1))
   (action  (with-stdout-to ${@}
diff --git a/doc/jbuild.rst b/doc/jbuild.rst
index 7026ff10e3a..571d413dfa1 100644
--- a/doc/jbuild.rst
+++ b/doc/jbuild.rst
@@ -711,6 +711,27 @@ With this jbuild file, running jbuilder as follow will replace the
 
     $ jbuilder build @runtest --auto-promote
 
+env
+---
+
+The ``env`` stanza allows to modify the environment. The syntax is as
+follow:
+
+.. code:: scheme
+
+     (env
+      (<profile1> <settings1>)
+      (<profile2> <settings2>)
+      ...
+      (<profilen> <settingsn>))
+
+The first form ``(<profile> <settings>)`` that correspond to the
+selected build profile will be used to modify the environment in this
+directory. You can use ``_`` to match any build profile.
+
+Currently ``<settings>`` can be any OCaml flags field, see `OCaml
+flags`_ for more details.
+
 Common items
 ============
 
@@ -1097,8 +1118,8 @@ The glob syntax is interpreted as follows:
 OCaml flags
 -----------
 
-In ``library`` and ``executables`` stanzas, you can specify OCaml compilation
-flags using the following fields:
+In ``library``, ``executable``, ``executables`` and ``env`` stanzas,
+you can specify OCaml compilation flags using the following fields:
 
 - ``(flags <flags>)`` to specify flags passed to both ``ocamlc`` and
   ``ocamlopt``
@@ -1108,16 +1129,14 @@ flags using the following fields:
 For all these fields, ``<flags>`` is specified in the `Ordered set language`_.
 These fields all support ``(:include ...)`` forms.
 
-The default value for ``(flags ...)`` includes some ``-w`` options to set
-warnings. The exact set depends on whether ``--dev`` is passed to Jbuilder. As a
-result it is recommended to write ``(flags ...)`` fields as follows:
+The default value for ``(flags ...)`` is taken from the environment,
+as a result it is recommended to write ``(flags ...)`` fields as
+follows:
 
-::
+.. code:: scheme
 
     (flags (:standard <my options>))
 
-.. _jbuild-jsoo:
-
 js_of_ocaml
 -----------
 
diff --git a/doc/quick-start.rst b/doc/quick-start.rst
index 55ad26757d7..ce8a9a22d83 100644
--- a/doc/quick-start.rst
+++ b/doc/quick-start.rst
@@ -116,6 +116,27 @@ Outside of the library, module ``Foo`` will be accessible as
 You can then use this library in any other directory by adding ``mylib``
 to the ``(libraries ...)`` field.
 
+Setting the OCaml compilation flags globally
+============================================
+
+Write this jbuild at the root of your project:
+
+.. code:: scheme
+
+    (env
+     (dev
+      (flags (:standard -w +42)))
+     (release
+      (flags (:standard -O3))))
+
+`dev` and `release` correspond to build profiles. The build profile
+can be selected from the command line with `--profile foo` or from a
+`dune-workspace` file by writing:
+
+.. code:: scheme
+
+    (profile foo)
+
 Using cppo
 ==========
 
diff --git a/doc/terminology.rst b/doc/terminology.rst
index cd373b48888..842effe759c 100644
--- a/doc/terminology.rst
+++ b/doc/terminology.rst
@@ -54,3 +54,19 @@ Terminology
    -  ``install`` which depends on everything that should be installed
    -  ``doc``     which depends on the generated HTML
       documentation. See :ref:`apidoc` for details
+
+- **environment**: in Jbuilder, each directory has an environment
+  attached to it. The environment determines the default values of
+  various parameters, such as the compilation flags. Inside a scope,
+  each directory inherit the environment from its parent. At the root
+  of every scope, a default environment is used. At any point, the
+  environment can be altered using an `env`_ stanza.
+
+- **build profile**: a global setting that influence various
+  defaults. It can be set from the command line using ``--profile
+  <profile>`` or from ``jbuild-workspace`` files. The following
+  profiles are standard:
+
+  -  ``default`` which is the default profile when none is set explicitely
+  -  ``release`` which is the profile used for opam releases
+  -  ``dev`` which has stricter warnings
diff --git a/doc/usage.rst b/doc/usage.rst
index d253f94bc6a..3c6241abfd6 100644
--- a/doc/usage.rst
+++ b/doc/usage.rst
@@ -225,8 +225,8 @@ follows:
 
     build: [["jbuilder" "build" "-p" name "-j" jobs]]
 
-``-p pkg`` is a shorthand for ``--root . --only-packages pkg --promote
-ignore``. ``-p`` is the short version of
+``-p pkg`` is a shorthand for ``--root . --only-packages pkg --profile
+release``. ``-p`` is the short version of
 ``--for-release-of-packages``.
 
 This has the following effects:
@@ -234,7 +234,7 @@ This has the following effects:
 -  it tells jbuilder to build everything that is installable and to
    ignore packages other than ``name`` defined in your project
 -  it sets the root to prevent jbuilder from looking it up
--  it ignores promotion to cut down dependencies and speed up the build
+-  it sets the build profile to ``release``
 -  it uses whatever concurrency option opam provides
 
 Note that ``name`` and ``jobs`` are variables expanded by opam. ``name``
@@ -355,6 +355,19 @@ as one containing exactly:
 This allows you to use an empty ``jbuild-workspace`` file to mark
 the root of your project.
 
+profile
+~~~~~~~
+
+The build profile can be selected in the ``jbuild-workspace`` file by
+write a ``(profile ...)`` stanza. For instance:
+
+.. code:: scheme
+
+    (profile dev)
+
+Note that the command line option ``--profile`` has precedence over
+this stanza.
+
 context
 ~~~~~~~
 
@@ -379,6 +392,10 @@ context or can be the description of an opam switch, as follows:
 - ``(merlin)`` instructs Jbuilder to use this build context for
    merlin
 
+- ``(profile <profile>)`` to set a different profile for a build
+  context. This has precedence over the command line option
+  ``--profile``
+
 Both ``(default ...)`` and ``(opam ...)`` accept a ``targets`` field
 in order to setup cross compilation. See `Cross Compilation`_ for more
 information.
diff --git a/src/build_system.ml b/src/build_system.ml
index ee14c68e10b..0594ecb9f6e 100644
--- a/src/build_system.ml
+++ b/src/build_system.ml
@@ -508,11 +508,8 @@ module Build_exec = struct
             reraise exn
     in
     let dyn_deps = ref Pset.empty in
-    let action = exec dyn_deps (Build.repr t) x in
-    (action, !dyn_deps)
-
-  let exec_nop bs t x =
-    snd (exec bs (Build.O.(>>^) t (fun () -> Action.Progn [])) x)
+    let result = exec dyn_deps (Build.repr t) x in
+    (result, !dyn_deps)
 end
 
 (* [copy_source] is [true] for rules copying files from the source directory *)
@@ -1206,8 +1203,10 @@ let eval_request t ~request ~process_target =
     (fun () ->
        wait_for_deps t rule_deps
        >>= fun () ->
-       let dyn_deps = Build_exec.exec_nop t request () in
-       process_targets (Pset.diff dyn_deps static_deps))
+       let result, dyn_deps = Build_exec.exec t request () in
+       process_targets (Pset.diff dyn_deps static_deps)
+       >>| fun () ->
+       result)
 
 let universe_file = Path.relative Path.build_dir ".universe-state"
 
diff --git a/src/build_system.mli b/src/build_system.mli
index 069aa47d2e9..d55c6a8f2dd 100644
--- a/src/build_system.mli
+++ b/src/build_system.mli
@@ -177,8 +177,8 @@ end with type build_system := t
 (** Do the actual build *)
 val do_build
   :  t
-  -> request:(unit, unit) Build.t
-  -> unit Fiber.t
+  -> request:(unit, 'a) Build.t
+  -> 'a Fiber.t
 
 (** {2 Other queries} *)
 
diff --git a/src/clflags.ml b/src/clflags.ml
index 2fdac5858cd..d10df6e78c4 100644
--- a/src/clflags.ml
+++ b/src/clflags.ml
@@ -3,7 +3,6 @@ let g = ref true
 let debug_findlib = ref false
 let warnings = ref "-40"
 let debug_dep_path = ref false
-let dev_mode = ref false
 let workspace_root = ref "."
 let external_lib_deps_hint = ref []
 let capture_outputs = ref true
diff --git a/src/clflags.mli b/src/clflags.mli
index 60a452cf893..e40cac0d4ef 100644
--- a/src/clflags.mli
+++ b/src/clflags.mli
@@ -15,9 +15,6 @@ val debug_findlib : bool ref
 (** Compiler warnings *)
 val warnings : string ref
 
-(** Whether we are compiling with extra warnings *)
-val dev_mode : bool ref
-
 (** The path to the workspace root *)
 val workspace_root : string ref
 
diff --git a/src/context.ml b/src/context.ml
index 12b3bdd87bf..6560203614e 100644
--- a/src/context.ml
+++ b/src/context.ml
@@ -21,6 +21,7 @@ end
 type t =
   { name                    : string
   ; kind                    : Kind.t
+  ; profile                 : string
   ; merlin                  : bool
   ; for_host                : t option
   ; implicit                : bool
@@ -81,6 +82,7 @@ let sexp_of_t t =
   record
     [ "name", string t.name
     ; "kind", Kind.sexp_of_t t.kind
+    ; "profile", string t.profile
     ; "merlin", bool t.merlin
     ; "for_host", option string (Option.map t.for_host ~f:(fun t -> t.name))
     ; "build_dir", path t.build_dir
@@ -128,7 +130,7 @@ let ocamlpath_sep =
   else
     Bin.path_sep
 
-let create ~(kind : Kind.t) ~path ~env ~name ~merlin ~targets () =
+let create ~(kind : Kind.t) ~path ~env ~name ~merlin ~targets ~profile () =
   let opam_var_cache = Hashtbl.create 128 in
   (match kind with
    | Opam { root; _ } ->
@@ -329,6 +331,7 @@ let create ~(kind : Kind.t) ~path ~env ~name ~merlin ~targets () =
       { name
       ; implicit
       ; kind
+      ; profile
       ; merlin
       ; for_host = host
       ; build_dir
@@ -407,7 +410,8 @@ let opam_config_var t var = opam_config_var ~env:t.env ~cache:t.opam_var_cache v
 let default ?(merlin=true) ~env ~targets () =
   create ~kind:Default ~path:Bin.path ~env ~name:"default" ~merlin ~targets ()
 
-let create_for_opam ?root ~env ~targets ~switch ~name ?(merlin=false) () =
+let create_for_opam ?root ~env ~targets ~profile ~switch ~name
+      ?(merlin=false) () =
   match Bin.opam with
   | None -> Utils.program_not_found "opam"
   | Some fn ->
@@ -444,13 +448,14 @@ let create_for_opam ?root ~env ~targets ~switch ~name ?(merlin=false) () =
       | Some s -> Bin.parse_path s
     in
     let env = Env.extend env ~vars in
-    create ~kind:(Opam { root; switch }) ~targets ~path ~env ~name ~merlin ()
+    create ~kind:(Opam { root; switch }) ~profile ~targets ~path ~env ~name
+      ~merlin ()
 
 let create ?merlin ~env def =
   match (def : Workspace.Context.t) with
-  | Default targets -> default ~env ~targets ?merlin ()
-  | Opam { name; switch; root; targets; _ } ->
-    create_for_opam ?root ~env ~switch ~name ?merlin ~targets ()
+  | Default { targets; profile } -> default ~env ~profile ~targets ?merlin ()
+  | Opam { name; switch; root; targets; profile; _ } ->
+    create_for_opam ?root ~env ~profile ~switch ~name ?merlin ~targets ()
 
 let which t s = which ~cache:t.which_cache ~path:t.path s
 
diff --git a/src/context.mli b/src/context.mli
index b3fcc57c679..733bd9d02a5 100644
--- a/src/context.mli
+++ b/src/context.mli
@@ -34,6 +34,8 @@ type t =
   { name : string
   ; kind : Kind.t
 
+  ; profile : string
+
   ; (** [true] if this context is used for the .merlin files *)
     merlin : bool
 
diff --git a/src/exe.ml b/src/exe.ml
index ed630bbb429..335413667f3 100644
--- a/src/exe.ml
+++ b/src/exe.ml
@@ -163,7 +163,7 @@ let link_exe
       Build.fanout
         (modules_and_cm_files >>^ snd)
         (SC.expand_and_eval_set sctx ~scope ~dir js_of_ocaml.flags
-           ~standard:(Js_of_ocaml_rules.standard ()))
+           ~standard:(Build.return (Js_of_ocaml_rules.standard sctx)))
     in
     SC.add_rules sctx (List.map rules ~f:(fun r -> cm_and_flags >>> r))
 
diff --git a/src/gen_rules.ml b/src/gen_rules.ml
index 9d38ebc9a5d..c1bfd953239 100644
--- a/src/gen_rules.ml
+++ b/src/gen_rules.ml
@@ -13,8 +13,7 @@ module Gen(P : Install_rules.Params) = struct
   module SC = Super_context
   module Odoc = Odoc.Gen(P)
 
-  open P
-
+  let sctx = P.sctx
   let ctx = SC.context sctx
 
   let stanzas_per_dir =
@@ -268,7 +267,8 @@ module Gen(P : Install_rules.Params) = struct
                   match (dep : Jbuild.Lib_dep.t) with
                   | Direct _ -> None
                   | Select s -> Some s.result_fn)
-              | Documentation _ | Alias _ | Provides _ | Install _ -> [])
+              | Documentation _ | Alias _ | Provides _ | Install _
+              | Env _ -> [])
             |> String.Set.of_list
           in
           String.Set.union generated_files
@@ -466,10 +466,12 @@ module Gen(P : Install_rules.Params) = struct
         (obj_deps
          >>>
          Build.fanout4
-           (top_sorted_modules >>^ artifacts ~ext:(Cm_kind.ext (Mode.cm_kind mode)))
-           (SC.expand_and_eval_set sctx ~scope ~dir lib.c_library_flags ~standard:[])
+           (top_sorted_modules >>^artifacts ~ext:(Cm_kind.ext (Mode.cm_kind mode)))
+           (SC.expand_and_eval_set sctx ~scope ~dir lib.c_library_flags
+              ~standard:(Build.return []))
            (Ocaml_flags.get flags mode)
-           (SC.expand_and_eval_set sctx ~scope ~dir lib.library_flags ~standard:[])
+           (SC.expand_and_eval_set sctx ~scope ~dir lib.library_flags
+              ~standard:(Build.return []))
          >>>
          Build.run ~context:ctx (Ok compiler)
            [ Dyn (fun (_, _, flags, _) -> As flags)
@@ -492,7 +494,7 @@ module Gen(P : Install_rules.Params) = struct
     let dst = Path.relative dir (c_name ^ ctx.ext_obj) in
     SC.add_rule sctx
       (SC.expand_and_eval_set sctx ~scope ~dir lib.c_flags
-         ~standard:(Context.cc_g ctx)
+         ~standard:(Build.return (Context.cc_g ctx))
        >>>
        Build.run ~context:ctx
          (* We have to execute the rule in the library directory as
@@ -519,7 +521,7 @@ module Gen(P : Install_rules.Params) = struct
     in
     SC.add_rule sctx
       (SC.expand_and_eval_set sctx ~scope ~dir lib.cxx_flags
-         ~standard:(Context.cc_g ctx)
+         ~standard:(Build.return (Context.cc_g ctx))
        >>>
        Build.run ~context:ctx
          (* We have to execute the rule in the library directory as
@@ -545,7 +547,7 @@ module Gen(P : Install_rules.Params) = struct
     let obj_dir = Utils.library_object_directory ~dir lib.name in
     let requires = Lib.Compile.requires compile_info in
     let dep_kind = if lib.optional then Build.Optional else Required in
-    let flags = Ocaml_flags.make lib.buildable sctx ~scope ~dir in
+    let flags = SC.ocaml_flags sctx ~scope ~dir lib.buildable in
     let { modules; main_module_name; alias_module } = modules_by_lib ~dir lib in
     let source_modules = modules in
     let already_used =
@@ -606,7 +608,7 @@ module Gen(P : Install_rules.Params) = struct
       ~js_of_ocaml ~dynlink ~flags ~scope ~dir ~obj_dir ~dep_graphs
       ~modules ~requires ~alias_module;
     Option.iter alias_module ~f:(fun m ->
-      let flags = Ocaml_flags.default () in
+      let flags = Ocaml_flags.default ~profile:(SC.profile sctx) in
       Module_compilation.build_module sctx m
         ~js_of_ocaml
         ~dynlink
@@ -650,7 +652,7 @@ module Gen(P : Install_rules.Params) = struct
         let ocamlmklib ~sandbox ~custom ~targets =
           SC.add_rule sctx ~sandbox
             (SC.expand_and_eval_set sctx ~scope ~dir
-               lib.c_library_flags ~standard:[]
+               lib.c_library_flags ~standard:(Build.return [])
              >>>
              Build.run ~context:ctx
                (Ok ctx.ocamlmklib)
@@ -858,14 +860,12 @@ module Gen(P : Install_rules.Params) = struct
         l
     in
 
-    let flags =
-      Ocaml_flags.make exes.buildable sctx ~scope ~dir
-    in
+    let flags = SC.ocaml_flags sctx ~scope ~dir exes.buildable in
     let link_flags =
       SC.expand_and_eval_set sctx exes.link_flags
         ~scope
         ~dir
-        ~standard:[]
+        ~standard:(Build.return [])
     in
 
     (* Use "eobjs" rather than "objs" to avoid a potential conflict
@@ -1027,6 +1027,7 @@ module type Gen = sig
     -> string list
     -> Build_system.extra_sub_directories_to_keep
   val init : unit -> unit
+  val sctx : Super_context.t
 end
 
 let gen ~contexts ~build_system
@@ -1084,11 +1085,11 @@ let gen ~contexts ~build_system
     let module M = Gen(struct let sctx = sctx end) in
     Fiber.Ivar.fill (Option.value_exn (Hashtbl.find sctxs context.name)) sctx
     >>| fun () ->
-    (context.name, ((module M : Gen), stanzas))
+    (context.name, (module M : Gen))
   in
   Fiber.parallel_map contexts ~f:make_sctx >>| fun l ->
   let map = String.Map.of_list_exn l in
   Build_system.set_rule_generators build_system
-    (String.Map.map map ~f:(fun ((module M : Gen), _) -> M.gen_rules));
-  String.Map.iter map ~f:(fun ((module M : Gen), _) -> M.init ());
-  String.Map.map map ~f:snd
+    (String_map.map map ~f:(fun (module M : Gen) -> M.gen_rules));
+  String_map.iter map ~f:(fun (module M : Gen) -> M.init ());
+  String_map.map map ~f:(fun (module M : Gen) -> M.sctx)
diff --git a/src/gen_rules.mli b/src/gen_rules.mli
index 65e4014d23c..6b2475e808c 100644
--- a/src/gen_rules.mli
+++ b/src/gen_rules.mli
@@ -1,5 +1,4 @@
 open! Import
-open Jbuild
 
 (* Generate rules. Returns evaluated jbuilds per context names. *)
 val gen
@@ -8,4 +7,4 @@ val gen
   -> ?external_lib_deps_mode:bool (* default: false *)
   -> ?only_packages:Package.Name.Set.t
   -> Jbuild_load.conf
-  -> (Path.t * Scope_info.t * Stanzas.t) list String.Map.t Fiber.t
+  -> Super_context.t String_map.t Fiber.t
diff --git a/src/inline_tests.ml b/src/inline_tests.ml
index cce6263832d..05d4efc222d 100644
--- a/src/inline_tests.ml
+++ b/src/inline_tests.ml
@@ -261,7 +261,7 @@ include Sub_system.Register_end_point(
             ~scope
             ~dir
             ~extra_vars
-            ~standard:[]))
+            ~standard:(Build.return [])))
       >>^ List.concat
     in
 
diff --git a/src/jbuild.ml b/src/jbuild.ml
index 49640fa1934..3fbec75bb6c 100644
--- a/src/jbuild.ml
+++ b/src/jbuild.ml
@@ -1192,6 +1192,42 @@ module Documentation = struct
       )
 end
 
+module Env = struct
+  type config =
+    { flags          : Ordered_set_lang.Unexpanded.t
+    ; ocamlc_flags   : Ordered_set_lang.Unexpanded.t
+    ; ocamlopt_flags : Ordered_set_lang.Unexpanded.t
+    }
+
+  type pattern =
+    | Profile of string
+    | Any
+
+  type t =
+    { loc   : Loc.t
+    ; rules : (pattern * config) list
+    }
+
+  let config =
+    record
+      (field_oslu "flags"          >>= fun flags          ->
+       field_oslu "ocamlc_flags"   >>= fun ocamlc_flags   ->
+       field_oslu "ocamlopt_flags" >>= fun ocamlopt_flags ->
+       return { flags; ocamlc_flags; ocamlopt_flags })
+
+  let rule = function
+    | List (loc, Atom (_, A pat) :: fields) ->
+      let pat =
+        match pat with
+        | "_" -> Any
+        | s   -> Profile s
+      in
+      (pat, config (List (loc, fields)))
+    | sexp ->
+      of_sexp_error sexp
+        "S-expression of the form (<profile> <fields>) expected"
+end
+
 module Stanza = struct
   type t =
     | Library     of Library.t
@@ -1203,6 +1239,7 @@ module Stanza = struct
     | Copy_files  of Copy_files.t
     | Menhir      of Menhir.t
     | Documentation of Documentation.t
+    | Env         of Env.t
 end
 
 module Stanzas = struct
@@ -1239,6 +1276,8 @@ module Stanzas = struct
           (fun glob -> [Copy_files {add_line_directive = false; glob}])
       ; cstr "copy_files#" (Copy_files.v1 @> nil)
           (fun glob -> [Copy_files {add_line_directive = true; glob}])
+      ; cstr_rest_loc "env" nil Env.rule
+          (fun loc rules -> [Env { loc; rules }])
       (* Just for validation and error messages *)
       ; cstr "jbuild_version" (Jbuild_version.t @> nil) (fun _ -> [])
       ; cstr_loc "include" (relative_file @> nil) (fun loc fn ->
@@ -1278,7 +1317,13 @@ module Stanzas = struct
       | _ :: (_, loc) :: _ ->
         Loc.fail loc "jbuild_version specified too many times"
     in
-    List.concat_map sexps ~f:(select version pkgs ~file ~include_stack)
+    let l =
+      List.concat_map sexps ~f:(select version pkgs ~file ~include_stack)
+    in
+    match List.filter_map l ~f:(function Env e -> Some e | _ -> None) with
+    | _ :: e :: _ ->
+      Loc.fail e.loc "The 'env' stanza cannot appear more than once"
+    | _ -> l
 
   let parse ?(default_version=Jbuild_version.latest_stable) ~file pkgs sexps =
     try
@@ -1302,16 +1347,4 @@ module Stanzas = struct
               sprintf
                 "\n--> included from %s"
                 (line_loc x))))
-
-  let lib_names ts =
-    List.fold_left ts ~init:String.Set.empty ~f:(fun acc (_, _, stanzas) ->
-      List.fold_left stanzas ~init:acc ~f:(fun acc -> function
-        | Stanza.Library lib ->
-          let acc =
-            match lib.public with
-             | None -> acc
-             | Some { name; _ } -> String.Set.add acc name
-          in
-          String.Set.add acc lib.name
-        | _ -> acc))
 end
diff --git a/src/jbuild.mli b/src/jbuild.mli
index ea8c9e898ba..7c1f843b375 100644
--- a/src/jbuild.mli
+++ b/src/jbuild.mli
@@ -369,6 +369,23 @@ module Documentation : sig
     }
 end
 
+module Env : sig
+  type config =
+    { flags          : Ordered_set_lang.Unexpanded.t
+    ; ocamlc_flags   : Ordered_set_lang.Unexpanded.t
+    ; ocamlopt_flags : Ordered_set_lang.Unexpanded.t
+    }
+
+  type pattern =
+    | Profile of string
+    | Any
+
+  type t =
+    { loc   : Loc.t
+    ; rules : (pattern * config) list
+    }
+end
+
 module Stanza : sig
   type t =
     | Library     of Library.t
@@ -380,6 +397,7 @@ module Stanza : sig
     | Copy_files  of Copy_files.t
     | Menhir      of Menhir.t
     | Documentation of Documentation.t
+    | Env         of Env.t
 end
 
 module Stanzas : sig
@@ -393,5 +411,4 @@ module Stanzas : sig
     -> Scope_info.t
     -> Sexp.Ast.t list
     -> t
-  val lib_names : (_ * _ * t) list -> String.Set.t
 end
diff --git a/src/js_of_ocaml_rules.ml b/src/js_of_ocaml_rules.ml
index 1b728398215..ffc49fb63bf 100644
--- a/src/js_of_ocaml_rules.ml
+++ b/src/js_of_ocaml_rules.ml
@@ -4,12 +4,14 @@ open Build.O
 
 module SC = Super_context
 
-let separate_compilation_enabled () = !Clflags.dev_mode
+let dev_mode sctx = SC.profile sctx = "dev"
 
-let pretty    () = if !Clflags.dev_mode then ["--pretty"           ] else []
-let sourcemap () = if !Clflags.dev_mode then ["--source-map-inline"] else []
+let separate_compilation_enabled = dev_mode
 
-let standard () = pretty () @ sourcemap ()
+let pretty    sctx = if dev_mode sctx then ["--pretty"           ] else []
+let sourcemap sctx = if dev_mode sctx then ["--source-map-inline"] else []
+
+let standard sctx = pretty sctx @ sourcemap sctx
 
 let install_jsoo_hint = "opam install js_of_ocaml-compiler"
 
@@ -95,18 +97,18 @@ let link_rule ~sctx ~dir ~runtime ~target ~requires =
     jsoo_link
     [ Arg_spec.A "-o"; Target target
     ; Arg_spec.Dep runtime
-    ; Arg_spec.As (sourcemap ())
+    ; Arg_spec.As (sourcemap sctx)
     ; Arg_spec.Dyn get_all
     ]
 
 let build_cm sctx ~scope ~dir ~(js_of_ocaml:Jbuild.Js_of_ocaml.t) ~src ~target =
-  if separate_compilation_enabled ()
+  if separate_compilation_enabled sctx
   then
     let itarget = Path.extend_basename src ~suffix:".js" in
     let spec = Arg_spec.Dep src in
     let flags =
       SC.expand_and_eval_set sctx ~scope ~dir js_of_ocaml.flags
-        ~standard:(standard ())
+        ~standard:(Build.return (standard sctx))
     in
     [ flags
       >>>
@@ -119,7 +121,7 @@ let build_cm sctx ~scope ~dir ~(js_of_ocaml:Jbuild.Js_of_ocaml.t) ~src ~target =
   else []
 
 let setup_separate_compilation_rules sctx components =
-  if separate_compilation_enabled ()
+  if separate_compilation_enabled sctx
   then
     match components with
     | [] | _ :: _ :: _ -> ()
@@ -145,7 +147,7 @@ let setup_separate_compilation_rules sctx components =
           let dir = in_build_dir ~ctx [ Lib.name pkg ] in
           let spec = Arg_spec.Dep src in
           SC.add_rule sctx
-            (Build.return (standard ())
+            (Build.return (standard sctx)
              >>>
              js_of_ocaml_rule ~sctx ~dir ~flags:(fun flags ->
                As flags) ~spec ~target)
@@ -157,7 +159,7 @@ let build_exe sctx ~dir ~js_of_ocaml ~src ~requires =
   let mk_target ext = Path.extend_basename src ~suffix:ext in
   let target = mk_target ".js" in
   let standalone_runtime = mk_target ".runtime.js" in
-  if separate_compilation_enabled () then
+  if separate_compilation_enabled sctx then
     [ link_rule ~sctx ~dir ~runtime:standalone_runtime ~target ~requires
     ; standalone_runtime_rule ~sctx ~dir ~javascript_files
         ~target:standalone_runtime ~requires
diff --git a/src/js_of_ocaml_rules.mli b/src/js_of_ocaml_rules.mli
index ccf1d1876e5..35c33a0d1ee 100644
--- a/src/js_of_ocaml_rules.mli
+++ b/src/js_of_ocaml_rules.mli
@@ -25,4 +25,4 @@ val setup_separate_compilation_rules
   -> string list
   -> unit
 
-val standard : unit -> string list
+val standard : Super_context.t -> string list
diff --git a/src/main.ml b/src/main.ml
index d886f5e1e65..5c3570727b2 100644
--- a/src/main.ml
+++ b/src/main.ml
@@ -5,8 +5,8 @@ let () = Inline_tests.linkme
 
 type setup =
   { build_system : Build_system.t
-  ; stanzas      : (Path.t * Jbuild.Scope_info.t * Jbuild.Stanzas.t) list String.Map.t
   ; contexts     : Context.t list
+  ; scontexts    : Super_context.t String_map.t
   ; packages     : Package.t Package.Name.Map.t
   ; file_tree    : File_tree.t
   ; env          : Env.t
@@ -36,6 +36,7 @@ let setup ?(log=Log.no_log)
       ?x
       ?ignore_promoted_rules
       ?(capture_outputs=true)
+      ?profile
       () =
   let env = setup_env ~capture_outputs in
   let conf =
@@ -57,7 +58,7 @@ let setup ?(log=Log.no_log)
     | None ->
       match workspace_file with
       | Some p ->
-        Workspace.load ?x p
+        Workspace.load ?x ?profile p
       | _ ->
         match
           List.find_map ["dune-workspace"; "jbuild-workspace"] ~f:(fun fn ->
@@ -67,14 +68,17 @@ let setup ?(log=Log.no_log)
             else
               None)
         with
-        | Some p -> Workspace.load ?x p
+        | Some p -> Workspace.load ?x ?profile p
         | None ->
           { merlin_context = Some "default"
-          ; contexts = [Default [
-              match x with
-              | None -> Native
-              | Some x -> Named x
-            ]]
+          ; contexts = [Default
+                          { targets = [
+                              match x with
+                              | None   -> Native
+                              | Some x -> Named x
+                            ]
+                          ; profile = Option.value profile ~default:"default"
+                          }]
           }
   in
 
@@ -104,12 +108,12 @@ let setup ?(log=Log.no_log)
     ~contexts
     ?only_packages
     ?external_lib_deps_mode
-  >>= fun stanzas ->
+  >>= fun scontexts ->
   Scheduler.set_status_line_generator gen_status_line
   >>>
   Fiber.return
     { build_system
-    ; stanzas
+    ; scontexts
     ; contexts
     ; packages = conf.packages
     ; file_tree = conf.file_tree
@@ -133,8 +137,8 @@ let external_lib_deps ?log ~packages () =
          | Ok path -> Path.append context.build_dir path
          | Error () -> die "Unknown package %S" (Package.Name.to_string pkg))
      in
-     let stanzas = Option.value_exn (String.Map.find setup.stanzas "default") in
-     let internals = Jbuild.Stanzas.lib_names stanzas in
+     let sctx = Option.value_exn (String.Map.find setup.scontexts "default") in
+     let internals = Super_context.internal_lib_names sctx in
      Path.Map.map
        (Build_system.all_lib_deps setup.build_system
           ~request:(Build.paths install_files))
@@ -220,9 +224,11 @@ let bootstrap () =
       | Error msg -> raise (Arg.Bad msg)
       | Ok c -> concurrency := Some c
     in
+    let profile = ref None in
     Arg.parse
       [ "-j"           , String concurrency_arg, "JOBS concurrency"
-      ; "--dev"        , Set Clflags.dev_mode  , " set development mode"
+      ; "--dev"        , Unit (fun () -> profile := Some "dev"),
+        " set development mode"
       ; "--display"    , display_mode          , " set the display mode"
       ; "--subst"      , Unit subst            ,
         " substitute watermarks in source files"
@@ -234,7 +240,7 @@ let bootstrap () =
     Clflags.debug_dep_path := true;
     let config =
       (* Only load the configuration with --dev *)
-      if !Clflags.dev_mode then
+      if !profile = Some "dev" then
         Config.load_user_config_file ()
       else
         Config.default
@@ -254,7 +260,14 @@ let bootstrap () =
       (set_concurrency config
        >>= fun () ->
        setup ~log ~workspace:{ merlin_context = Some "default"
-                             ; contexts = [Default [Native]] }
+                             ; contexts = [Default { targets = [Native]
+                                                   ; profile =
+                                                       Option.value !profile
+                                                         ~default:"default"
+                                                   }
+                                          ]
+                             }
+         ?profile:!profile
          ~extra_ignored_subtrees:ignored_during_bootstrap
          ()
        >>= fun { build_system = bs; _ } ->
diff --git a/src/main.mli b/src/main.mli
index 8b559d884bf..c56ff5923df 100644
--- a/src/main.mli
+++ b/src/main.mli
@@ -1,11 +1,9 @@
 open! Import
-open Jbuild
 
 type setup =
   { build_system : Build_system.t
-  ; (* Evaluated jbuilds per context names *)
-    stanzas      : (Path.t * Scope_info.t * Stanzas.t) list String.Map.t
   ; contexts     : Context.t list
+  ; scontexts    : Super_context.t String_map.t
   ; packages     : Package.t Package.Name.Map.t
   ; file_tree    : File_tree.t
   ; env          : Env.t
@@ -25,6 +23,7 @@ val setup
   -> ?x:string
   -> ?ignore_promoted_rules:bool
   -> ?capture_outputs:bool
+  -> ?profile:string
   -> unit
   -> setup Fiber.t
 val external_lib_deps
diff --git a/src/menhir.ml b/src/menhir.ml
index 92c7230ed8c..570aba8486d 100644
--- a/src/menhir.ml
+++ b/src/menhir.ml
@@ -24,7 +24,10 @@ module SC = Super_context
 let gen_rules sctx ~dir ~scope (t : Jbuild.Menhir.t) =
   let targets n = List.map ~f:(Path.relative dir) [n ^ ".ml"; n ^ ".mli"] in
   (* This expands special variables such as ${ROOT} in the flags *)
-  let flags = SC.expand_and_eval_set sctx ~scope ~dir t.flags ~standard:[] in
+  let flags =
+    SC.expand_and_eval_set sctx ~scope ~dir t.flags
+      ~standard:(Build.return [])
+  in
   let menhir_binary =
     SC.resolve_program sctx "menhir" ~hint:"opam install menhir"
   in
diff --git a/src/ocaml_flags.ml b/src/ocaml_flags.ml
index e079e93ed0e..653992356f7 100644
--- a/src/ocaml_flags.ml
+++ b/src/ocaml_flags.ml
@@ -21,8 +21,8 @@ let dev_mode_warnings =
        ; 60
        ])
 
-let default_flags () =
-  if !Clflags.dev_mode then
+let default_flags ~profile =
+  if profile = "dev" then
     [ "-w"; dev_mode_warnings ^ !Clflags.warnings
     ; "-strict-sequence"
     ; "-strict-formats"
@@ -46,12 +46,26 @@ let empty =
 let of_list l =
   { empty with common = Build.arr (fun () -> l) }
 
-let make { Jbuild.Buildable. flags; ocamlc_flags; ocamlopt_flags; _ } ctx ~scope ~dir =
-  let eval = Super_context.expand_and_eval_set ctx ~scope ~dir in
-  { common   = Build.memoize "common flags" (eval flags ~standard:(default_flags ()))
+let default ~profile =
+  { common = Build.return (default_flags ~profile)
   ; specific =
-      { byte   = Build.memoize "ocamlc flags" (eval ocamlc_flags   ~standard:(default_ocamlc_flags ()))
-      ; native = Build.memoize "ocamlopt flags" (eval ocamlopt_flags ~standard:(default_ocamlopt_flags ()))
+      { byte   = Build.return (default_ocamlc_flags   ())
+      ; native = Build.return (default_ocamlopt_flags ())
+      }
+  }
+
+let make ~flags ~ocamlc_flags ~ocamlopt_flags ~default ~eval =
+  let f name x standard =
+    Build.memoize name
+      (if Ordered_set_lang.Unexpanded.has_special_forms x then
+         eval x ~standard
+       else
+         eval x ~standard:(Build.return []))
+  in
+  { common = f "common flags" flags default.common
+  ; specific =
+      { byte   = f "ocamlc flags"   ocamlc_flags   default.specific.byte
+      ; native = f "ocamlopt flags" ocamlopt_flags default.specific.native
       }
   }
 
@@ -64,16 +78,17 @@ let get t mode =
 
 let get_for_cm t ~cm_kind = get t (Mode.of_cm_kind cm_kind)
 
-let default () =
-  { common = Build.return (default_flags ())
-  ; specific =
-      { byte   = Build.return (default_ocamlc_flags   ())
-      ; native = Build.return (default_ocamlopt_flags ())
-      }
-  }
-
 let append_common t flags = {t with common = t.common >>^ fun l -> l @ flags}
 
 let prepend_common flags t = {t with common = t.common >>^ fun l -> flags @ l}
 
 let common t = t.common
+
+let dump t =
+  Build.fanout3 t.common t.specific.byte t.specific.native
+  >>^ fun (common, byte, native) ->
+  List.map ~f:Sexp.To_sexp.(pair string (list string))
+    [  "flags"         , common
+    ; "ocamlc_flags"   , byte
+    ; "ocamlopt_flags" , native
+    ]
diff --git a/src/ocaml_flags.mli b/src/ocaml_flags.mli
index 51ddaf6d10b..fa9b1d4d0f3 100644
--- a/src/ocaml_flags.mli
+++ b/src/ocaml_flags.mli
@@ -5,13 +5,16 @@ open Stdune
 type t
 
 val make
-  :  Jbuild.Buildable.t
-  -> Super_context.t
-  -> scope:Scope.t
-  -> dir:Path.t
+  :  flags          : Ordered_set_lang.Unexpanded.t
+  -> ocamlc_flags   : Ordered_set_lang.Unexpanded.t
+  -> ocamlopt_flags : Ordered_set_lang.Unexpanded.t
+  -> default:t
+  -> eval:(Ordered_set_lang.Unexpanded.t
+           -> standard:(unit, string list) Build.t
+           -> (unit, string list) Build.t)
   -> t
 
-val default : unit -> t
+val default : profile:string -> t
 
 val empty : t
 
@@ -24,3 +27,5 @@ val append_common : t -> string list -> t
 val prepend_common : string list -> t -> t
 
 val common : t -> (unit, string list) Build.t
+
+val dump : t -> (unit, Sexp.t list) Build.t
diff --git a/src/ordered_set_lang.ml b/src/ordered_set_lang.ml
index 29c2293abf8..2d8ca438ae2 100644
--- a/src/ordered_set_lang.ml
+++ b/src/ordered_set_lang.ml
@@ -223,6 +223,20 @@ module Unexpanded = struct
     in
     loop String.Set.empty t.ast
 
+  let has_special_forms t =
+    let rec loop (t : ast) =
+      let open Ast in
+      match t with
+      | Special _ | Include _ -> true
+      | Element _ -> false
+      | Union l ->
+        List.exists l ~f:loop
+      | Diff (l, r) ->
+        loop l ||
+        loop r
+    in
+    loop t.ast
+
   let expand t ~files_contents ~f  =
     let rec expand (t : ast) : ast_expanded =
       let open Ast in
diff --git a/src/ordered_set_lang.mli b/src/ordered_set_lang.mli
index 77e15f60532..010de4c3e3c 100644
--- a/src/ordered_set_lang.mli
+++ b/src/ordered_set_lang.mli
@@ -58,6 +58,8 @@ module Unexpanded : sig
 
   val field : ?default:t -> string -> t Sexp.Of_sexp.record_parser
 
+  val has_special_forms : t -> bool
+
   (** List of files needed to expand this set *)
   val files : t -> f:(String_with_vars.t -> string) -> String.Set.t
 
diff --git a/src/super_context.ml b/src/super_context.ml
index 50d7b1917ee..993b5515fea 100644
--- a/src/super_context.ml
+++ b/src/super_context.ml
@@ -14,6 +14,16 @@ module Dir_with_jbuild = struct
     }
 end
 
+module Env_node = struct
+  type t =
+    { dir                 : Path.t
+    ; inherit_from        : t Lazy.t option
+    ; scope               : Scope.t
+    ; config              : Env.t
+    ; mutable ocaml_flags : Ocaml_flags.t option
+    }
+end
+
 type t =
   { context                          : Context.t
   ; build_system                     : Build_system.t
@@ -30,6 +40,7 @@ type t =
   ; chdir                            : (Action.t, Action.t) Build.t
   ; host                             : t option
   ; libs_by_package : (Package.t * Lib.Set.t) Package.Name.Map.t
+  ; env                              : (Path.t, Env_node.t) Hashtbl.t
   }
 
 let context t = t.context
@@ -41,10 +52,23 @@ let file_tree t = t.file_tree
 let stanzas_to_consider_for_install t = t.stanzas_to_consider_for_install
 let cxx_flags t = t.cxx_flags
 let build_dir t = t.context.build_dir
+let profile t = t.context.profile
 let build_system t = t.build_system
 
 let host t = Option.value t.host ~default:t
 
+let internal_lib_names t =
+  List.fold_left t.stanzas ~init:String.Set.empty
+    ~f:(fun acc { Dir_with_jbuild. stanzas; _ } ->
+      List.fold_left stanzas ~init:acc ~f:(fun acc -> function
+        | Stanza.Library lib ->
+          String.Set.add
+            (match lib.public with
+             | None -> acc
+             | Some { name; _ } -> String.Set.add acc name)
+            lib.name
+        | _ -> acc))
+
 let public_libs    t = t.public_libs
 let installed_libs t = t.installed_libs
 
@@ -64,6 +88,88 @@ let expand_vars t ~scope ~dir ?(extra_vars=String.Map.empty) s =
          | Some _ as x -> x
          | None -> String.Map.find extra_vars var))
 
+let expand_and_eval_set t ~scope ~dir ?extra_vars set ~standard =
+  let open Build.O in
+  let f = expand_vars t ~scope ~dir ?extra_vars in
+  let parse ~loc:_ s = s in
+  match Ordered_set_lang.Unexpanded.files set ~f |> String.Set.to_list with
+  | [] ->
+    let set =
+      Ordered_set_lang.Unexpanded.expand set ~files_contents:String.Map.empty ~f
+    in
+    standard >>^ fun standard ->
+    Ordered_set_lang.String.eval set ~standard ~parse
+  | files ->
+    let paths = List.map files ~f:(Path.relative dir) in
+    Build.fanout standard (Build.all (List.map paths ~f:Build.read_sexp))
+    >>^ fun (standard, sexps) ->
+    let files_contents = List.combine files sexps |> String.Map.of_list_exn in
+    let set = Ordered_set_lang.Unexpanded.expand set ~files_contents ~f in
+    Ordered_set_lang.String.eval set ~standard ~parse
+
+module Env = struct
+  open Env_node
+
+  let rec get t ~dir =
+    match Hashtbl.find t.env dir with
+    | None ->
+      if Path.is_root dir then raise_notrace Exit;
+      let node = get t ~dir:(Path.parent dir) in
+      Hashtbl.add t.env dir node;
+      node
+    | Some node -> node
+
+  let get t ~dir =
+    match get t ~dir with
+    | node -> node
+    | exception Exit ->
+      Exn.code_error "Super_context.Env.get called on invalid directory"
+        [ "dir", Path.sexp_of_t dir ]
+
+  let ocaml_flags t ~dir =
+    let rec loop t node =
+      match node.ocaml_flags with
+      | Some x -> x
+      | None ->
+        let default =
+          match node.inherit_from with
+          | None -> Ocaml_flags.default ~profile:(profile t)
+          | Some (lazy node) -> loop t node
+        in
+        let flags =
+          match List.find_map node.config.rules ~f:(fun (pat, cfg) ->
+            match (pat : Env.pattern), profile t with
+            | Any, _ -> Some cfg
+            | Profile a, b -> Option.some_if (a = b) cfg)
+          with
+          | None -> default
+          | Some cfg ->
+            Ocaml_flags.make
+              ~flags:cfg.flags
+              ~ocamlc_flags:cfg.ocamlc_flags
+              ~ocamlopt_flags:cfg.ocamlopt_flags
+              ~default
+              ~eval:(expand_and_eval_set t ~scope:node.scope ~dir:node.dir
+                       ?extra_vars:None)
+        in
+        node.ocaml_flags <- Some flags;
+        flags
+    in
+    loop t (get t ~dir)
+
+end
+
+let ocaml_flags t ~dir ~scope (x : Buildable.t) =
+  Ocaml_flags.make
+    ~flags:x.flags
+    ~ocamlc_flags:x.ocamlc_flags
+    ~ocamlopt_flags:x.ocamlopt_flags
+    ~default:(Env.ocaml_flags t ~dir)
+    ~eval:(expand_and_eval_set t ~scope ~dir ?extra_vars:None)
+
+let dump_env t ~dir =
+  Ocaml_flags.dump (Env.ocaml_flags t ~dir)
+
 let resolve_program t ?hint bin =
   Artifacts.binary ?hint t.artifacts bin
 
@@ -189,34 +295,65 @@ let create
     | Ok    x -> x
     | Error _ -> assert false
   in
-  { context
-  ; host
-  ; build_system
-  ; scopes
-  ; public_libs
-  ; installed_libs
-  ; stanzas
-  ; packages
-  ; file_tree
-  ; stanzas_to_consider_for_install
-  ; artifacts
-  ; cxx_flags
-  ; vars
-  ; chdir = Build.arr (fun (action : Action.t) ->
-      match action with
-      | Chdir _ -> action
-      | _ -> Chdir (context.build_dir, action))
-  ; libs_by_package =
-    Lib.DB.all public_libs
-    |> Lib.Set.to_list
-    |> List.map ~f:(fun lib ->
-      (Option.value_exn (Lib.package lib), lib))
-    |> Package.Name.Map.of_list_multi
-    |> Package.Name.Map.merge packages ~f:(fun _name pkg libs ->
-      let pkg  = Option.value_exn pkg          in
-      let libs = Option.value libs ~default:[] in
-      Some (pkg, Lib.Set.of_list libs))
-  }
+  let t =
+    { context
+    ; host
+    ; build_system
+    ; scopes
+    ; public_libs
+    ; installed_libs
+    ; stanzas
+    ; packages
+    ; file_tree
+    ; stanzas_to_consider_for_install
+    ; artifacts
+    ; cxx_flags
+    ; vars
+    ; chdir = Build.arr (fun (action : Action.t) ->
+        match action with
+        | Chdir _ -> action
+        | _ -> Chdir (context.build_dir, action))
+    ; libs_by_package =
+        Lib.DB.all public_libs
+        |> Lib.Set.to_list
+        |> List.map ~f:(fun lib ->
+          (Option.value_exn (Lib.package lib), lib))
+        |> Package.Name.Map.of_list_multi
+        |> Package.Name.Map.merge packages ~f:(fun _name pkg libs ->
+          let pkg  = Option.value_exn pkg          in
+          let libs = Option.value libs ~default:[] in
+          Some (pkg, Lib.Set.of_list libs))
+    ; env = Hashtbl.create 128
+    }
+  in
+  List.iter stanzas
+    ~f:(fun { Dir_with_jbuild. ctx_dir; scope; stanzas; _ } ->
+      List.iter stanzas ~f:(function
+        | Stanza.Env config ->
+          let inherit_from =
+            if ctx_dir = Scope.root scope then
+              None
+            else
+              Some (lazy (Env.get t ~dir:(Path.parent ctx_dir)))
+          in
+          Hashtbl.add t.env ctx_dir
+            { dir          = ctx_dir
+            ; inherit_from = inherit_from
+            ; scope        = scope
+            ; config       = config
+            ; ocaml_flags  = None
+            }
+        | _ -> ()));
+  if not (Hashtbl.mem t.env context.build_dir) then
+    Hashtbl.add t.env context.build_dir
+      { Env_node.
+        dir          = context.build_dir
+      ; inherit_from = None
+      ; scope        = Scope.DB.find_by_dir scopes context.build_dir
+      ; config       = { loc = Loc.none; rules = [] }
+      ; ocaml_flags  = None
+      };
+  t
 
 let prefix_rules t prefix ~f =
   Build_system.prefix_rules t.build_system prefix ~f
@@ -695,21 +832,3 @@ module Action = struct
     | [] -> build
     | fail :: _ -> Build.fail fail >>> build
 end
-
-let expand_and_eval_set t ~scope ~dir ?extra_vars set ~standard =
-  let open Build.O in
-  let f = expand_vars t ~scope ~dir ?extra_vars in
-  let parse ~loc:_ s = s in
-  match Ordered_set_lang.Unexpanded.files set ~f |> String.Set.to_list with
-  | [] ->
-    let set =
-      Ordered_set_lang.Unexpanded.expand set ~files_contents:String.Map.empty ~f
-    in
-    Build.return (Ordered_set_lang.String.eval set ~standard ~parse)
-  | files ->
-    let paths = List.map files ~f:(Path.relative dir) in
-    Build.all (List.map paths ~f:Build.read_sexp)
-    >>^ fun sexps ->
-    let files_contents = List.combine files sexps |> String.Map.of_list_exn in
-    let set = Ordered_set_lang.Unexpanded.expand set ~files_contents ~f in
-    Ordered_set_lang.String.eval set ~standard ~parse
diff --git a/src/super_context.mli b/src/super_context.mli
index 8e0ebd8d3c2..8ec0286e2d7 100644
--- a/src/super_context.mli
+++ b/src/super_context.mli
@@ -40,6 +40,7 @@ val artifacts : t -> Artifacts.t
 val stanzas_to_consider_for_install : t -> (Path.t * Scope.t * Stanza.t) list
 val cxx_flags : t -> string list
 val build_dir : t -> Path.t
+val profile   : t -> string
 val host : t -> t
 val build_system : t -> Build_system.t
 
@@ -49,6 +50,21 @@ val public_libs : t -> Lib.DB.t
 (** Installed libraries that are not part of the workspace *)
 val installed_libs : t -> Lib.DB.t
 
+(** All non-public library names *)
+val internal_lib_names : t -> String.Set.t
+
+(** Compute the ocaml flags based on the directory environment and a
+    buildable stanza *)
+val ocaml_flags
+  :  t
+  -> dir:Path.t
+  -> scope:Scope.t
+  -> Buildable.t
+  -> Ocaml_flags.t
+
+(** Dump a directory environment in a readable form *)
+val dump_env : t -> dir:Path.t -> (unit, Sexp.t list) Build.t
+
 val find_scope_by_dir  : t -> Path.t        -> Scope.t
 val find_scope_by_name : t -> string option -> Scope.t
 
@@ -66,14 +82,15 @@ val expand_and_eval_set
   -> dir:Path.t
   -> ?extra_vars:Action.Var_expansion.t String.Map.t
   -> Ordered_set_lang.Unexpanded.t
-  -> standard:string list
+  -> standard:(unit, string list) Build.t
   -> (unit, string list) Build.t
 
 val prefix_rules
-  : t
+  :  t
   -> (unit, unit) Build.t
   -> f:(unit -> 'a)
   -> 'a
+
 val add_rule
   :  t
   -> ?sandbox:bool
diff --git a/src/utop.ml b/src/utop.ml
index 13394971f56..b8ab074e77a 100644
--- a/src/utop.ml
+++ b/src/utop.ml
@@ -78,6 +78,8 @@ let setup sctx ~dir ~(libs : Library.t list) ~scope =
       ~scope
       ~linkages:[Exe.Linkage.custom]
       ~requires
-      ~flags:(Ocaml_flags.append_common (Ocaml_flags.default ()) ["-w"; "-24"])
+      ~flags:(Ocaml_flags.append_common
+                (Ocaml_flags.default ~profile:(Super_context.profile sctx))
+                ["-w"; "-24"])
       ~link_flags:(Build.return ["-linkall"; "-warn-error"; "-31"]);
     add_module_rules sctx ~dir:utop_exe_dir requires
diff --git a/src/workspace.ml b/src/workspace.ml
index fc7b2f89f5b..7af6068b1ba 100644
--- a/src/workspace.ml
+++ b/src/workspace.ml
@@ -16,39 +16,57 @@ module Context = struct
   module Opam = struct
     type t =
       { name    : string
+      ; profile : string
       ; switch  : string
       ; root    : string option
       ; merlin  : bool
       ; targets : Target.t list
       }
 
-    let t =
+    let t ~profile =
       field   "switch"  string                                    >>= fun switch ->
       field   "name"    string ~default:switch                    >>= fun name ->
       field   "targets" (list Target.t) ~default:[Target.Native]  >>= fun targets ->
       field_o "root"    string                                    >>= fun root ->
       field_b "merlin"                                            >>= fun merlin ->
+      field   "profile" string ~default:profile                   >>= fun profile ->
       return { switch
              ; name
              ; root
              ; merlin
              ; targets
+             ; profile
              }
   end
 
-  type t = Default of Target.t list | Opam of Opam.t
+  module Default = struct
+    type t =
+      { profile : string
+      ; targets : Target.t list
+      }
 
-  let t = function
-    | Atom (_, A "default") -> Default [Native]
-    | List (_, List _ :: _) as sexp -> Opam (record Opam.t sexp)
+    let t ~profile =
+      field "targets" (list Target.t) ~default:[Target.Native]
+      >>= fun targets ->
+      field "profile" string ~default:profile
+      >>= fun profile ->
+      return { targets; profile }
+  end
+
+  type t = Default of Default.t | Opam of Opam.t
+
+  let t ~profile = function
+    | Atom (_, A "default") ->
+      Default { targets = [Native]
+              ; profile
+              }
+    | List (_, List _ :: _) as sexp -> Opam (record (Opam.t ~profile) sexp)
     | sexp ->
       sum
         [ cstr_record "default"
-            (field "targets" (list Target.t) ~default:[Target.Native]
-             >>= fun targets ->
-             return (Default targets))
+            (Default.t ~profile >>= fun x -> return (Default x))
         ; cstr_record "opam"
-            (Opam.t >>= fun x -> return (Opam x))
+            (Opam.t ~profile >>= fun x -> return (Opam x))
         ]
         sexp
 
@@ -57,8 +75,8 @@ module Context = struct
     | Opam    o -> o.name
 
   let targets = function
-    | Default l -> l
-    | Opam    o -> o.targets
+    | Default x -> x.targets
+    | Opam    x -> x.targets
 
   let all_names t =
     let n = name t in
@@ -72,15 +90,38 @@ type t =
   ; contexts       : Context.t list
   }
 
-let t ?x sexps =
+type item = Context of Sexp.Ast.t | Profile of Loc.t * string
+
+let item_of_sexp =
+  sum
+    [ cstr "context" (raw @> nil) (fun x -> Context x)
+    ; cstr_loc "profile" (string @> nil) (fun loc x -> Profile (loc, x))
+    ]
+
+let t ?x ?profile:cmdline_profile sexps =
   let defined_names = ref String.Set.empty in
-  let merlin_ctx, contexts =
-    List.fold_left sexps ~init:(None, []) ~f:(fun (merlin_ctx, ctxs) sexp ->
-      let ctx =
-        sum
-          [ cstr "context" (Context.t @> nil) (fun x -> x) ]
-          sexp
-      in
+  let profiles, contexts =
+    List.partition_map sexps ~f:(fun sexp ->
+      match item_of_sexp sexp with
+      | Profile (loc, p) -> Left (loc, p)
+      | Context c -> Right c)
+  in
+  let profile =
+    match profiles, cmdline_profile with
+    | _ :: (loc, _) :: _, _ ->
+      Loc.fail loc "profile defined too many times"
+    | _, Some p -> p
+    | [], None -> "default"
+    | [(_, p)], None -> p
+  in
+  let { merlin_context; contexts } =
+    let init =
+      { merlin_context = None
+      ; contexts       = []
+      }
+    in
+    List.fold_left contexts ~init ~f:(fun t sexp ->
+      let ctx = Context.t ~profile sexp in
       let ctx =
         match x with
         | None -> ctx
@@ -93,8 +134,10 @@ let t ?x sexps =
               targets @ [target]
           in
           match ctx with
-          | Default targets -> Default (add_target target targets)
-          | Opam o -> Opam { o with targets = add_target target o.targets }
+          | Default d ->
+            Default { d with targets = add_target target d.targets }
+          | Opam o ->
+            Opam    { o with targets = add_target target o.targets }
       in
       let name = Context.name ctx in
       if name = "" ||
@@ -108,22 +151,22 @@ let t ?x sexps =
         of_sexp_errorf sexp "second definition of build context %S" name;
       defined_names := String.Set.union !defined_names
                          (String.Set.of_list (Context.all_names ctx));
-      match ctx, merlin_ctx with
+      match ctx, t.merlin_context with
       | Opam { merlin = true; _ }, Some _ ->
         of_sexp_errorf sexp "you can only have one context for merlin"
       | Opam { merlin = true; _ }, None ->
-        (Some name, ctx :: ctxs)
+        { merlin_context = Some name; contexts = ctx :: t.contexts }
       | _ ->
-        (merlin_ctx, ctx :: ctxs))
+        { t with contexts = ctx :: t.contexts })
   in
   let contexts =
     match contexts with
-    | [] -> [Context.Default [Native]]
+    | [] -> [Context.Default { targets = [Native]; profile }]
     | _  -> contexts
   in
-  let merlin_ctx =
-    match merlin_ctx with
-    | Some _ -> merlin_ctx
+  let merlin_context =
+    match merlin_context with
+    | Some _ -> merlin_context
     | None ->
       if List.exists contexts
            ~f:(function Context.Default _ -> true | _ -> false) then
@@ -131,8 +174,8 @@ let t ?x sexps =
       else
         None
   in
-  { merlin_context = merlin_ctx
-  ; contexts       = List.rev contexts
+  { merlin_context
+  ; contexts = List.rev contexts
   }
 
-let load ?x p = t ?x (Io.Sexp.load p ~mode:Many)
+let load ?x ?profile p = t ?x ?profile (Io.Sexp.load p ~mode:Many)
diff --git a/src/workspace.mli b/src/workspace.mli
index d4bac52e0c7..fb7c346e929 100644
--- a/src/workspace.mli
+++ b/src/workspace.mli
@@ -10,15 +10,23 @@ module Context : sig
   end
   module Opam : sig
     type t =
-      { name   : string
-      ; switch : string
-      ; root   : string option
-      ; merlin : bool
+      { name    : string
+      ; profile : string
+      ; switch  : string
+      ; root    : string option
+      ; merlin  : bool
       ; targets : Target.t list
       }
   end
 
-  type t = Default of Target.t list | Opam of Opam.t
+  module Default : sig
+    type t =
+      { profile : string
+      ; targets : Target.t list
+      }
+  end
+
+  type t = Default of Default.t | Opam of Opam.t
 
   val name : t -> string
 end
@@ -28,4 +36,4 @@ type t =
   ; contexts       : Context.t list
   }
 
-val load : ?x:string -> Path.t -> t
+val load : ?x:string -> ?profile:string -> Path.t -> t
diff --git a/test/blackbox-tests/dune.inc b/test/blackbox-tests/dune.inc
index f366d6876b1..f8dbff41e92 100644
--- a/test/blackbox-tests/dune.inc
+++ b/test/blackbox-tests/dune.inc
@@ -57,6 +57,14 @@
     test-cases/depend-on-the-universe
     (progn (run ${exe:cram.exe} -test run.t) (diff? run.t run.t.corrected))))))
 
+(alias
+ ((name env)
+  (deps ((package dune) (files_recursively_in test-cases/env)))
+  (action
+   (chdir
+    test-cases/env
+    (progn (run ${exe:cram.exe} -test run.t) (diff? run.t run.t.corrected))))))
+
 (alias
  ((name exclude-missing-module)
   (deps
@@ -444,6 +452,7 @@
     (alias copy_files)
     (alias cross-compilation)
     (alias depend-on-the-universe)
+    (alias env)
     (alias exclude-missing-module)
     (alias exec-cmd)
     (alias findlib)
@@ -496,6 +505,7 @@
     (alias copy_files)
     (alias cross-compilation)
     (alias depend-on-the-universe)
+    (alias env)
     (alias exclude-missing-module)
     (alias exec-cmd)
     (alias findlib)
diff --git a/test/blackbox-tests/test-cases/env/bin/jbuild b/test/blackbox-tests/test-cases/env/bin/jbuild
new file mode 100644
index 00000000000..3ea8a9f15a7
--- /dev/null
+++ b/test/blackbox-tests/test-cases/env/bin/jbuild
@@ -0,0 +1,3 @@
+(env
+ (default
+  (flags (-machin))))
diff --git a/test/blackbox-tests/test-cases/env/jbuild b/test/blackbox-tests/test-cases/env/jbuild
new file mode 100644
index 00000000000..10a480440d0
--- /dev/null
+++ b/test/blackbox-tests/test-cases/env/jbuild
@@ -0,0 +1,3 @@
+(env
+ (default
+  (flags (:standard -plop))))
diff --git a/test/blackbox-tests/test-cases/env/run.t b/test/blackbox-tests/test-cases/env/run.t
new file mode 100644
index 00000000000..3f9588ed6d3
--- /dev/null
+++ b/test/blackbox-tests/test-cases/env/run.t
@@ -0,0 +1,36 @@
+  $ dune printenv .
+  (
+   (flags (-w -40 -plop))
+   (ocamlc_flags (-g))
+   (ocamlopt_flags (-g))
+  )
+  $ dune printenv src
+  (
+   (flags (-w -40 -plop -truc))
+   (ocamlc_flags (-g))
+   (ocamlopt_flags (-g))
+  )
+  $ dune printenv bin
+  (
+   (flags (-machin))
+   (ocamlc_flags (-g))
+   (ocamlopt_flags (-g))
+  )
+  $ dune printenv vendor
+  (
+   (flags (-w -40 -plop))
+   (ocamlc_flags (-g))
+   (ocamlopt_flags (-g))
+  )
+  $ dune printenv vendor/a
+  (
+   (flags (-w -40 -bidule))
+   (ocamlc_flags (-g))
+   (ocamlopt_flags (-g))
+  )
+  $ dune printenv vendor/a/src
+  (
+   (flags (-w -40 -bidule -pouet))
+   (ocamlc_flags (-g))
+   (ocamlopt_flags (-g))
+  )
diff --git a/test/blackbox-tests/test-cases/env/src/jbuild b/test/blackbox-tests/test-cases/env/src/jbuild
new file mode 100644
index 00000000000..750f0be1757
--- /dev/null
+++ b/test/blackbox-tests/test-cases/env/src/jbuild
@@ -0,0 +1,3 @@
+(env
+ (default
+  (flags (:standard -truc))))
diff --git a/test/blackbox-tests/test-cases/env/vendor/a/a.opam b/test/blackbox-tests/test-cases/env/vendor/a/a.opam
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/env/vendor/a/jbuild b/test/blackbox-tests/test-cases/env/vendor/a/jbuild
new file mode 100644
index 00000000000..4d10c80c795
--- /dev/null
+++ b/test/blackbox-tests/test-cases/env/vendor/a/jbuild
@@ -0,0 +1,3 @@
+(env
+ (default
+  (flags (:standard -bidule))))
diff --git a/test/blackbox-tests/test-cases/env/vendor/a/src/jbuild b/test/blackbox-tests/test-cases/env/vendor/a/src/jbuild
new file mode 100644
index 00000000000..3721468f9cf
--- /dev/null
+++ b/test/blackbox-tests/test-cases/env/vendor/a/src/jbuild
@@ -0,0 +1,3 @@
+(env
+ (default
+  (flags (:standard -pouet))))