diff --git a/doc/pyproject_toml.rst b/doc/pyproject_toml.rst
index 2fa18ed3..c8daf0ce 100644
--- a/doc/pyproject_toml.rst
+++ b/doc/pyproject_toml.rst
@@ -67,12 +67,23 @@ requires
             "configparser; python_version == '2.7'"
       ]
 
+extras-require
+  Lists of packages needed for every optional feature. The requirements
+  are specified in the same format as for ``requires``. The requirements of
+  the two reserved extras ``test`` and ``doc`` as well as the extra ``dev``
+  are installed by ``flit install``. For example:
+
+  .. code-block:: toml
+
+      [tool.flit.metadata.extras-require]
+      test = ["pytest>=2.7.3", "pytest-cov"]
+      doc = ["sphinx"]
+
 dev-requires
-  Packages that are required for development. This field is in the same format
-  as ``requires``.
+  Packages that are required for development, other than the ones belonging to
+  the extras ``test`` and ``doc``. This field is in the same format as ``requires``.
 
-  These are not (yet) encoded in the wheel, but are used when doing
-  ``flit install``.
+  These are installed by ``flit install`` and encoded in the wheel as extra ``dev``.
 description-file
   A path (relative to the .toml file) to a file containing a longer description
   of your package to show on PyPI. This should be written in `reStructuredText
diff --git a/flit/common.py b/flit/common.py
index b73ebc96..ad2e7cb1 100644
--- a/flit/common.py
+++ b/flit/common.py
@@ -227,17 +227,23 @@ class Metadata:
     requires_external = ()
     provides_extra = ()
 
-    metadata_version="2.1"
+    metadata_version = "2.1"
 
-    # this is part of metadata spec 2, we are using it for installation but it
-    # doesn't actually get written to the metadata file
+    # metadata spec 2
     dev_requires = ()
+    extras_require = {}
 
     def __init__(self, data):
         self.name = data.pop('name')
         self.version = data.pop('version')
         self.author_email = data.pop('author_email')
         self.summary = data.pop('summary')
+        self.extras_require = data.pop('extras_require', {})
+        dev_requires = data.pop('dev_requires', None)
+        if dev_requires is not None:
+            self.extras_require['dev'] = dev_requires
+        explicit_extras = data.pop('provides_extra', ())
+        self.provides_extra = list(set(explicit_extras) | self.extras_require.keys())
         for k, v in data.items():
             assert hasattr(self, k), "data does not have attribute '{}'".format(k)
             setattr(self, k, v)
@@ -280,6 +286,10 @@ def write_metadata_file(self, fp):
         for req in self.requires_dist:
             fp.write('Requires-Dist: {}\n'.format(req))
 
+        for extra, reqs in self.extras_require.items():
+            for req in reqs:
+                fp.write('Requires-Dist: {}; extra == "{}"\n'.format(req, extra))
+
         for url in self.project_urls:
             fp.write('Project-URL: {}\n'.format(url))
 
diff --git a/flit/inifile.py b/flit/inifile.py
index 1920bd2b..0a45b44b 100644
--- a/flit/inifile.py
+++ b/flit/inifile.py
@@ -34,6 +34,7 @@ class ConfigError(ValueError):
     'dist-name',
     'entry-points-file',
     'description-file',
+    'extras-require',
 } | metadata_list_fields
 
 metadata_required_fields = {