diff --git a/src/wormhole/_boss.py b/src/wormhole/_boss.py
index 33c00e2..c99bb3d 100644
--- a/src/wormhole/_boss.py
+++ b/src/wormhole/_boss.py
@@ -32,6 +32,7 @@ class Boss(object):
     _url = attrib(validator=instance_of(type(u"")))
     _appid = attrib(validator=instance_of(type(u"")))
     _versions = attrib(validator=instance_of(dict))
+    _client_version = attrib(validator=instance_of(tuple))
     _reactor = attrib()
     _journal = attrib(validator=provides(_interfaces.IJournal))
     _tor = attrib(validator=optional(provides(_interfaces.ITorManager)))
@@ -52,7 +53,8 @@ class Boss(object):
         self._R = Receive(self._side, self._timing)
         self._RC = RendezvousConnector(self._url, self._appid, self._side,
                                        self._reactor, self._journal,
-                                       self._tor, self._timing)
+                                       self._tor, self._timing,
+                                       self._client_version)
         self._L = Lister(self._timing)
         self._A = Allocator(self._timing)
         self._I = Input(self._timing)
diff --git a/src/wormhole/_rendezvous.py b/src/wormhole/_rendezvous.py
index 28a64cd..963d12a 100644
--- a/src/wormhole/_rendezvous.py
+++ b/src/wormhole/_rendezvous.py
@@ -67,6 +67,7 @@ class RendezvousConnector(object):
     _journal = attrib(validator=provides(_interfaces.IJournal))
     _tor = attrib(validator=optional(provides(_interfaces.ITorManager)))
     _timing = attrib(validator=provides(_interfaces.ITiming))
+    _client_version = attrib(validator=instance_of(tuple))
 
     def __attrs_post_init__(self):
         self._have_made_a_successful_connection = False
@@ -165,7 +166,8 @@ class RendezvousConnector(object):
         self._have_made_a_successful_connection = True
         self._ws = proto
         try:
-            self._tx("bind", appid=self._appid, side=self._side)
+            self._tx("bind", appid=self._appid, side=self._side,
+                     client_version=self._client_version)
             self._N.connected()
             self._M.connected()
             self._L.connected()
diff --git a/src/wormhole/test/test_machines.py b/src/wormhole/test/test_machines.py
index 52a2d0c..ec96fc0 100644
--- a/src/wormhole/test/test_machines.py
+++ b/src/wormhole/test/test_machines.py
@@ -5,7 +5,7 @@ from zope.interface import directlyProvides, implementer
 from twisted.trial import unittest
 from .. import (errors, timing, _order, _receive, _key, _code, _lister, _boss,
                 _input, _allocator, _send, _terminator, _nameplate, _mailbox,
-                _rendezvous)
+                _rendezvous, __version__)
 from .._interfaces import (IKey, IReceive, IBoss, ISend, IMailbox, IOrder,
                            IRendezvousConnector, ILister, IInput, IAllocator,
                            INameplate, ICode, IWordlist, ITerminator)
@@ -1219,8 +1219,9 @@ class Boss(unittest.TestCase):
         reactor = None
         journal = ImmediateJournal()
         tor_manager = None
+        client_version = ("python", __version__)
         b = MockBoss(wormhole, "side", "url", "appid", versions,
-                     reactor, journal, tor_manager,
+                     client_version, reactor, journal, tor_manager,
                      timing.DebugTiming())
         b._T = Dummy("t", events, ITerminator, "close")
         b._S = Dummy("s", events, ISend, "send")
@@ -1449,10 +1450,12 @@ class Rendezvous(unittest.TestCase):
         reactor = object()
         journal = ImmediateJournal()
         tor_manager = None
+        client_version = ("python", __version__)
         rc = _rendezvous.RendezvousConnector("ws://host:4000/v1", "appid",
                                              "side", reactor,
                                              journal, tor_manager,
-                                             timing.DebugTiming())
+                                             timing.DebugTiming(),
+                                             client_version)
         b = Dummy("b", events, IBoss, "error")
         n = Dummy("n", events, INameplate, "connected", "lost")
         m = Dummy("m", events, IMailbox, "connected", "lost")
@@ -1501,8 +1504,9 @@ class Rendezvous(unittest.TestCase):
                 self.assertEqual(c[1][1], False, ws.mock_calls)
                 yield bytes_to_dict(c[1][0])
         self.assertEqual(list(sent_messages(ws)),
-                         [dict(appid="appid", side="side", id="0000",
-                               type="bind"),
+                         [dict(appid="appid", side="side",
+                               client_version=["python", __version__],
+                               id="0000", type="bind"),
                           ])
 
         rc.ws_close(True, None, None)
diff --git a/src/wormhole/wormhole.py b/src/wormhole/wormhole.py
index 72feb07..311e3fc 100644
--- a/src/wormhole/wormhole.py
+++ b/src/wormhole/wormhole.py
@@ -3,6 +3,7 @@ import os, sys
 from attr import attrs, attrib
 from zope.interface import implementer
 from twisted.python import failure
+from . import __version__
 from ._interfaces import IWormhole, IDeferredWormhole
 from .util import bytes_to_hexstr
 from .eventual import EventualQueue
@@ -230,8 +231,12 @@ def create(appid, relay_url, reactor, # use keyword args for everything else
         w = _DeferredWormhole(eq)
     wormhole_versions = {} # will be used to indicate Wormhole capabilities
     wormhole_versions["app_versions"] = versions # app-specific capabilities
-    b = Boss(w, side, relay_url, appid, wormhole_versions,
-             reactor, journal, tor, timing)
+    v = __version__
+    if isinstance(v, type(b"")):
+        v = v.decode("utf-8", errors="replace")
+    client_version = ("python", v)
+    b = Boss(w, side, relay_url, appid, wormhole_versions, client_version,
+                reactor, journal, tor, timing)
     w._set_boss(b)
     b.start()
     return w