diff --git a/tensorboard/BUILD b/tensorboard/BUILD
index a09a7a5ac2..e89b1206d4 100644
--- a/tensorboard/BUILD
+++ b/tensorboard/BUILD
@@ -419,6 +419,7 @@ py_library(
     srcs_version = "PY2AND3",
     visibility = ["//visibility:public"],
     deps = [
+        "//tensorboard/backend:experiment_id",
         "@org_mozilla_bleach",
         "@org_pythonhosted_markdown",
         "@org_pythonhosted_six",
@@ -434,6 +435,7 @@ py_test(
     deps = [
         ":plugin_util",
         ":test",
+        "//tensorboard/backend:experiment_id",
         "@org_pythonhosted_six",
     ],
 )
diff --git a/tensorboard/backend/BUILD b/tensorboard/backend/BUILD
index 0bcc8bc12f..fb5eaa83fb 100644
--- a/tensorboard/backend/BUILD
+++ b/tensorboard/backend/BUILD
@@ -63,6 +63,7 @@ py_library(
     visibility = ["//visibility:public"],
     deps = [
         ":empty_path_redirect",
+        ":experiment_id",
         ":http_util",
         ":path_prefix",
         "//tensorboard:errors",
@@ -91,6 +92,7 @@ py_test(
     deps = [
         ":application",
         "//tensorboard:errors",
+        "//tensorboard:plugin_util",
         "//tensorboard:test",
         "//tensorboard/backend/event_processing:event_multiplexer",
         "//tensorboard/plugins:base_plugin",
@@ -118,6 +120,23 @@ py_test(
     ],
 )
 
+py_library(
+    name = "experiment_id",
+    srcs = ["experiment_id.py"],
+    srcs_version = "PY2AND3",
+)
+
+py_test(
+    name = "experiment_id_test",
+    srcs = ["experiment_id_test.py"],
+    srcs_version = "PY2AND3",
+    deps = [
+        ":experiment_id",
+        "//tensorboard:test",
+        "@org_pocoo_werkzeug",
+    ],
+)
+
 py_library(
     name = "path_prefix",
     srcs = ["path_prefix.py"],
diff --git a/tensorboard/backend/application.py b/tensorboard/backend/application.py
index 0c35a780d8..c9c17d9b41 100644
--- a/tensorboard/backend/application.py
+++ b/tensorboard/backend/application.py
@@ -40,6 +40,7 @@
 
 from tensorboard import errors
 from tensorboard.backend import empty_path_redirect
+from tensorboard.backend import experiment_id
 from tensorboard.backend import http_util
 from tensorboard.backend import path_prefix
 from tensorboard.backend.event_processing import db_import_multiplexer
@@ -331,6 +332,7 @@ def _create_wsgi_app(self):
     """Apply middleware to create the final WSGI app."""
     app = self._route_request
     app = empty_path_redirect.EmptyPathRedirectMiddleware(app)
+    app = experiment_id.ExperimentIdMiddleware(app)
     app = path_prefix.PathPrefixMiddleware(app, self._path_prefix)
     app = _handling_errors(app)
     return app
@@ -429,6 +431,7 @@ def _route_request(self, environ, start_response):
       environ: See WSGI spec (PEP 3333).
       start_response: See WSGI spec (PEP 3333).
     """
+
     request = wrappers.Request(environ)
     parsed_url = urlparse.urlparse(request.path)
     clean_path = _clean_path(parsed_url.path)
diff --git a/tensorboard/backend/application_test.py b/tensorboard/backend/application_test.py
index d1a2b740cf..e34d96603a 100644
--- a/tensorboard/backend/application_test.py
+++ b/tensorboard/backend/application_test.py
@@ -41,6 +41,7 @@
 from werkzeug import wrappers
 
 from tensorboard import errors
+from tensorboard import plugin_util
 from tensorboard import test as tb_test
 from tensorboard.backend import application
 from tensorboard.backend.event_processing import plugin_event_multiplexer as event_multiplexer  # pylint: disable=line-too-long
@@ -621,6 +622,11 @@ def setUp(self):
                     '/wildcard/special/exact': self._foo_handler,
                 },
                 construction_callback=self._construction_callback),
+            FakePluginLoader(
+                plugin_name='whoami',
+                routes_mapping={
+                    '/eid': self._eid_handler,
+                }),
         ],
         dummy_assets_zip_provider)
 
@@ -641,6 +647,12 @@ def _foo_handler(self, request):
   def _bar_handler(self):
     pass
 
+  @wrappers.Request.application
+  def _eid_handler(self, request):
+    eid = plugin_util.experiment_id(request.environ)
+    body = json.dumps({'experiment_id': eid})
+    return wrappers.Response(body, 200, content_type='application/json')
+
   @wrappers.Request.application
   def _wildcard_handler(self, request):
     if request.path == '/data/plugin/bar/wildcard/ok':
@@ -664,11 +676,12 @@ def testPluginsAdded(self):
     self.assertLessEqual(expected_routes, frozenset(self.app.exact_routes))
 
   def testNameToPluginMapping(self):
-    # The mapping from plugin name to instance should include both plugins.
+    # The mapping from plugin name to instance should include all plugins.
     mapping = self.context.plugin_name_to_instance
-    self.assertItemsEqual(['foo', 'bar'], list(mapping.keys()))
+    self.assertItemsEqual(['foo', 'bar', 'whoami'], list(mapping.keys()))
     self.assertEqual('foo', mapping['foo'].plugin_name)
     self.assertEqual('bar', mapping['bar'].plugin_name)
+    self.assertEqual('whoami', mapping['whoami'].plugin_name)
 
   def testNormalRoute(self):
     self._test_route('/data/plugin/foo/foo_route', 200)
@@ -679,6 +692,18 @@ def testNormalRouteIsNotWildcard(self):
   def testMissingRoute(self):
     self._test_route('/data/plugin/foo/bogus', 404)
 
+  def testExperimentIdIntegration_withNoExperimentId(self):
+    response = self.server.get('/data/plugin/whoami/eid')
+    self.assertEqual(response.status_code, 200)
+    data = json.loads(response.get_data().decode('utf-8'))
+    self.assertEqual(data, {'experiment_id': ''})
+
+  def testExperimentIdIntegration_withExperimentId(self):
+    response = self.server.get('/experiment/123/data/plugin/whoami/eid')
+    self.assertEqual(response.status_code, 200)
+    data = json.loads(response.get_data().decode('utf-8'))
+    self.assertEqual(data, {'experiment_id': '123'})
+
   def testEmptyRoute(self):
     self._test_route('', 301)
 
diff --git a/tensorboard/backend/experiment_id.py b/tensorboard/backend/experiment_id.py
new file mode 100644
index 0000000000..7c427abe32
--- /dev/null
+++ b/tensorboard/backend/experiment_id.py
@@ -0,0 +1,71 @@
+# Copyright 2019 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Application-level experiment ID support."""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import re
+
+
+# Value of the first path component that signals that the second path
+# component represents an experiment ID.
+_EXPERIMENT_PATH_COMPONENT = "experiment"
+
+# Key into the WSGI environment used for the experiment ID.
+WSGI_ENVIRON_KEY = "HTTP_TENSORBOARD_EXPERIMENT_ID"
+
+
+class ExperimentIdMiddleware(object):
+  """WSGI middleware extracting experiment IDs from URL to environment.
+
+  Any request whose path matches `/experiment/SOME_EID[/...]` will have
+  its first two path components stripped, and its experiment ID stored
+  onto the WSGI environment with key taken from the `WSGI_ENVIRON_KEY`
+  constant. All other requests will have paths unchanged and the
+  experiment ID set to the empty string.
+
+  Instances of this class are WSGI applications (see PEP 3333).
+  """
+
+  def __init__(self, application):
+    """Initializes an `ExperimentIdMiddleware`.
+
+    Args:
+      application: The WSGI application to wrap (see PEP 3333).
+    """
+    self._application = application
+    # Regular expression that matches the whole `/experiment/EID` prefix
+    # (without any trailing slash) and captures the experiment ID.
+    self._pat = re.compile(
+        r"/%s/([^/]*)" % re.escape(_EXPERIMENT_PATH_COMPONENT)
+    )
+
+  def __call__(self, environ, start_response):
+    path = environ.get("PATH_INFO", "")
+    m = self._pat.match(path)
+    if m:
+      eid = m.group(1)
+      new_path = path[m.end(0):]
+      root = m.group(0)
+    else:
+      eid = ""
+      new_path = path
+      root = ""
+    environ[WSGI_ENVIRON_KEY] = eid
+    environ["PATH_INFO"] = new_path
+    environ["SCRIPT_NAME"] = environ.get("SCRIPT_NAME", "") + root
+    return self._application(environ, start_response)
diff --git a/tensorboard/backend/experiment_id_test.py b/tensorboard/backend/experiment_id_test.py
new file mode 100644
index 0000000000..4e8a85a129
--- /dev/null
+++ b/tensorboard/backend/experiment_id_test.py
@@ -0,0 +1,80 @@
+# Copyright 2019 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Tests for `tensorboard.backend.experiment_id`."""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import json
+
+import werkzeug
+
+from tensorboard import test as tb_test
+from tensorboard.backend import experiment_id
+
+
+class ExperimentIdMiddlewareTest(tb_test.TestCase):
+  """Tests for `ExperimentIdMiddleware`."""
+
+  def setUp(self):
+    super(ExperimentIdMiddlewareTest, self).setUp()
+    self.app = experiment_id.ExperimentIdMiddleware(self._echo_app)
+    self.server = werkzeug.test.Client(self.app, werkzeug.BaseResponse)
+
+  def _echo_app(self, environ, start_response):
+    # https://www.python.org/dev/peps/pep-0333/#environ-variables
+    data = {
+        "eid": environ[experiment_id.WSGI_ENVIRON_KEY],
+        "path": environ.get("PATH_INFO", ""),
+        "script": environ.get("SCRIPT_NAME", ""),
+    }
+    body = json.dumps(data, sort_keys=True)
+    start_response("200 OK", [("Content-Type", "application/json")])
+    return [body]
+
+  def _assert_ok(self, response, eid, path, script):
+    self.assertEqual(response.status_code, 200)
+    actual = json.loads(response.get_data())
+    expected = dict(eid=eid, path=path, script=script)
+    self.assertEqual(actual, expected)
+
+  def test_no_experiment_empty_path(self):
+    response = self.server.get("")
+    self._assert_ok(response, eid="", path="", script="")
+
+  def test_no_experiment_root_path(self):
+    response = self.server.get("/")
+    self._assert_ok(response, eid="", path="/", script="")
+
+  def test_no_experiment_sub_path(self):
+    response = self.server.get("/x/y")
+    self._assert_ok(response, eid="", path="/x/y", script="")
+
+  def test_with_experiment_empty_path(self):
+    response = self.server.get("/experiment/123")
+    self._assert_ok(response, eid="123", path="", script="/experiment/123")
+
+  def test_with_experiment_root_path(self):
+    response = self.server.get("/experiment/123/")
+    self._assert_ok(response, eid="123", path="/", script="/experiment/123")
+
+  def test_with_experiment_sub_path(self):
+    response = self.server.get("/experiment/123/x/y")
+    self._assert_ok(response, eid="123", path="/x/y", script="/experiment/123")
+
+
+if __name__ == "__main__":
+  tb_test.main()
diff --git a/tensorboard/plugin_util.py b/tensorboard/plugin_util.py
index d1dfef5ccf..c259f001d2 100644
--- a/tensorboard/plugin_util.py
+++ b/tensorboard/plugin_util.py
@@ -24,6 +24,9 @@
 import markdown
 import six
 
+from tensorboard.backend import experiment_id as _experiment_id
+
+
 _ALLOWED_ATTRIBUTES = {
     'a': ['href', 'title'],
     'img': ['src', 'title', 'alt'],
@@ -85,3 +88,20 @@ def markdown_to_safe_html(markdown_string):
   string_sanitized = bleach.clean(
       string_html, tags=_ALLOWED_TAGS, attributes=_ALLOWED_ATTRIBUTES)
   return warning + string_sanitized
+
+
+def experiment_id(environ):
+  """Determine the experiment ID associated with a WSGI request.
+
+  Each request to TensorBoard has an associated experiment ID, which is
+  always a string and may be empty. This experiment ID should be passed
+  to data providers.
+
+  Args:
+    environ: A WSGI environment `dict`. For a Werkzeug request, this is
+      `request.environ`.
+
+  Returns:
+    A experiment ID, as a possibly-empty `str`.
+  """
+  return environ.get(_experiment_id.WSGI_ENVIRON_KEY, "")
diff --git a/tensorboard/plugin_util_test.py b/tensorboard/plugin_util_test.py
index 320c78348f..ae029ccb67 100644
--- a/tensorboard/plugin_util_test.py
+++ b/tensorboard/plugin_util_test.py
@@ -22,6 +22,7 @@
 
 from tensorboard import plugin_util
 from tensorboard import test as tb_test
+from tensorboard.backend import experiment_id
 
 
 class MarkdownToSafeHTMLTest(tb_test.TestCase):
@@ -123,5 +124,19 @@ def test_null_bytes_stripped_before_markdown_processing(self):
                '<p>un_der_score</p>')
 
 
+class ExperimentIdTest(tb_test.TestCase):
+  """Tests for `plugin_util.experiment_id`."""
+
+  def test_default(self):
+    # This shouldn't happen; the `ExperimentIdMiddleware` always set an
+    # experiment ID. In case something goes wrong, degrade gracefully.
+    environ = {}
+    self.assertEqual(plugin_util.experiment_id(environ), "")
+
+  def test_present(self):
+    environ = {experiment_id.WSGI_ENVIRON_KEY: "123"}
+    self.assertEqual(plugin_util.experiment_id(environ), "123")
+
+
 if __name__ == '__main__':
   tb_test.main()