diff --git a/CHANGES.rst b/CHANGES.rst
index 1055a2f0..5321b177 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,3 +1,10 @@
+v5.8.0
+======
+
+* #250: Now ``Traversable.joinpath`` provides a concrete
+  implementation, replacing the implementation in ``.simple``
+  and converging with the behavior in ``MultiplexedPath``.
+
 v5.7.1
 ======
 
diff --git a/importlib_resources/abc.py b/importlib_resources/abc.py
index 5e38ba61..efa86ac6 100644
--- a/importlib_resources/abc.py
+++ b/importlib_resources/abc.py
@@ -1,5 +1,7 @@
 import abc
 import io
+import itertools
+import pathlib
 from typing import Any, BinaryIO, Iterable, Iterator, NoReturn, Text, Optional
 
 from ._compat import runtime_checkable, Protocol, StrPath
@@ -50,6 +52,10 @@ def contents(self) -> Iterable[str]:
         raise FileNotFoundError
 
 
+class TraversalError(Exception):
+    pass
+
+
 @runtime_checkable
 class Traversable(Protocol):
     """
@@ -92,7 +98,6 @@ def is_file(self) -> bool:
         Return True if self is a file
         """
 
-    @abc.abstractmethod
     def joinpath(self, *descendants: StrPath) -> "Traversable":
         """
         Return Traversable resolved with any descendants applied.
@@ -101,6 +106,22 @@ def joinpath(self, *descendants: StrPath) -> "Traversable":
         and each may contain multiple levels separated by
         ``posixpath.sep`` (``/``).
         """
+        if not descendants:
+            return self
+        names = itertools.chain.from_iterable(
+            path.parts for path in map(pathlib.PurePosixPath, descendants)
+        )
+        target = next(names)
+        matches = (
+            traversable for traversable in self.iterdir() if traversable.name == target
+        )
+        try:
+            match = next(matches)
+        except StopIteration:
+            raise TraversalError(
+                "Target not found during traversal.", target, list(names)
+            )
+        return match.joinpath(*names)
 
     def __truediv__(self, child: StrPath) -> "Traversable":
         """
diff --git a/importlib_resources/readers.py b/importlib_resources/readers.py
index f1190ca4..19450f46 100644
--- a/importlib_resources/readers.py
+++ b/importlib_resources/readers.py
@@ -82,15 +82,16 @@ def is_dir(self):
     def is_file(self):
         return False
 
-    def joinpath(self, child):
-        # first try to find child in current paths
-        for file in self.iterdir():
-            if file.name == child:
-                return file
-        # if it does not exist, construct it with the first path
-        return self._paths[0] / child
-
-    __truediv__ = joinpath
+    def joinpath(self, *descendants):
+        try:
+            return super().joinpath(*descendants)
+        except abc.TraversalError as exc:
+            # One of the paths didn't resolve.
+            msg, target, names = exc.args
+            if names:  # pragma: nocover
+                raise
+            # It was the last; construct result with the first path.
+            return self._paths[0].joinpath(target)
 
     def open(self, *args, **kwargs):
         raise FileNotFoundError(f'{self} is not a file')
diff --git a/importlib_resources/simple.py b/importlib_resources/simple.py
index d0fbf237..b85e4694 100644
--- a/importlib_resources/simple.py
+++ b/importlib_resources/simple.py
@@ -99,20 +99,6 @@ def iterdir(self):
     def open(self, *args, **kwargs):
         raise IsADirectoryError()
 
-    @staticmethod
-    def _flatten(compound_names):
-        for name in compound_names:
-            yield from name.split('/')
-
-    def joinpath(self, *descendants):
-        if not descendants:
-            return self
-        names = self._flatten(descendants)
-        target = next(names)
-        return next(
-            traversable for traversable in self.iterdir() if traversable.name == target
-        ).joinpath(*names)
-
 
 class TraversableReader(TraversableResources, SimpleReader):
     """
diff --git a/importlib_resources/tests/test_reader.py b/importlib_resources/tests/test_reader.py
index 16841a50..37550cad 100644
--- a/importlib_resources/tests/test_reader.py
+++ b/importlib_resources/tests/test_reader.py
@@ -75,6 +75,7 @@ def test_join_path(self):
             str(path.joinpath('imaginary'))[len(prefix) + 1 :],
             os.path.join('namespacedata01', 'imaginary'),
         )
+        self.assertEqual(path.joinpath(), path)
 
     def test_repr(self):
         self.assertEqual(