diff --git a/plugins/NickAuth/plugin.py b/plugins/NickAuth/plugin.py
index c84d56b35..b8116dbc6 100644
--- a/plugins/NickAuth/plugin.py
+++ b/plugins/NickAuth/plugin.py
@@ -147,6 +147,13 @@ class NickAuth(callbacks.Plugin):
         irc.queueMsg(ircmsgs.whois(nick, nick))
     auth = wrap(auth, [])
 
+    def inFilter(self, irc, msg):
+        """If the messages has a server tag with account name, tries to
+        authenticate it."""
+        if msg.server_tags and 'account' in msg.server_tags:
+            self._auth(irc, msg.prefix, msg.server_tags['account'])
+        return msg
+
     def do330(self, irc, msg):
         mynick, theirnick, theiraccount, garbage = msg.args
         # I would like to use a dict comprehension, but we have to support
@@ -176,18 +183,8 @@ class NickAuth(callbacks.Plugin):
         account = msg.args[0]
         user = ircdb.users.getUserFromNick(irc.network, account)
 
-        if not user:
-            try:
-                user = ircdb.users.getUser(msg.prefix)
-            except KeyError:
-                user = None
-
-        if user:
-            if account == '*':
-                user.clearAuth()
-            else:
-                user.addAuth(msg.prefix)
-                ircdb.users.setUser(user, flush=False)
+        if account != '*':
+            self._auth(irc, msg.prefix, account)
 
 
     def doJoin(self, irc, msg):
@@ -196,18 +193,8 @@ class NickAuth(callbacks.Plugin):
             return
 
         account = msg.args[1]
-        user = ircdb.users.getUserFromNick(irc.network, account)
-
-        if not user:
-            try:
-                user = ircdb.users.getUser(msg.prefix)
-            except KeyError:
-                user = None
-
-        if user:
-            if account != '*':
-                user.addAuth(msg.prefix)
-                ircdb.users.setUser(user, flush=False)
+        if account != '*':
+            self._auth(irc, msg.prefix, account)
 
     def do354(self, irc, msg):
         if len(msg.args) != 6 or msg.args[1] != '1':
@@ -217,6 +204,12 @@ class NickAuth(callbacks.Plugin):
         prefix = '%s!%s@%s' % (nick, ident, host)
         user = ircdb.users.getUserFromNick(irc.network, account)
 
+        if account != '0':
+            self._auth(irc, prefix, account)
+
+    def _auth(self, irc, prefix, account):
+        user = ircdb.users.getUserFromNick(irc.network, account)
+
         if not user:
             try:
                 user = ircdb.users.getUser(prefix)
@@ -224,7 +217,6 @@ class NickAuth(callbacks.Plugin):
                 user = None
 
         if user:
-            if account != '0':
                 user.addAuth(prefix)
                 ircdb.users.setUser(user, flush=False)
 
diff --git a/plugins/NickCapture/plugin.py b/plugins/NickCapture/plugin.py
index 17b312204..974d50657 100644
--- a/plugins/NickCapture/plugin.py
+++ b/plugins/NickCapture/plugin.py
@@ -45,6 +45,12 @@ class NickCapture(callbacks.Plugin):
         self.__parent = super(NickCapture, self)
         self.__parent.__init__(irc)
         self.lastIson = 0
+        self.monitoring = []
+
+    def die(self):
+        for irc in self.monitoring:
+            nick = self._getNick(irc.network)
+            irc.unmonitor(nick)
         
     def _getNick(self, network):
         network_nick = conf.supybot.networks.get(network).nick()
@@ -60,10 +66,16 @@ class NickCapture(callbacks.Plugin):
                 # We used to check this, but nicksToHostmasks is never cleared
                 # except on reconnects, which can cause trouble.
                 # if nick not in irc.state.nicksToHostmasks:
-                self._ison(irc, nick)
+                if 'monitor' in irc.state.supported:
+                    if irc not in self.monitoring:
+                        irc.monitor(nick)
+                        self.monitoring.append(irc)
+                else:
+                    self._ison(irc, nick)
                 self.__parent.__call__(irc, msg)
 
     def _ison(self, irc, nick):
+        assert 'monitor' not in irc.state.supported
         if self.registryValue('ison'):
             now = time.time()
             if now - self.lastIson > self.registryValue('ison.period'):
@@ -95,6 +107,16 @@ class NickCapture(callbacks.Plugin):
             nick = self._getNick(irc.network)
             if nick:
                 self._sendNick(irc, nick)
+
+    def do731(self, irc, msg):
+        """This is sent by the MONITOR when a nick goes offline."""
+        nick = self._getNick(irc.network)
+        for target in msg.args[1].split(','):
+            if nick == target:
+                self._sendNick(irc, nick)
+                self.monitoring.remove(irc)
+                irc.unmonitor(nick)
+                break
 NickCapture = internationalizeDocstring(NickCapture)
 
 Class = NickCapture
diff --git a/src/irclib.py b/src/irclib.py
index 94380f9b2..ee122084c 100644
--- a/src/irclib.py
+++ b/src/irclib.py
@@ -666,6 +666,7 @@ class Irc(IrcCommandDispatcher):
         self._setNonResettingVariables()
         self._queueConnectMessages()
         self.startedSync = ircutils.IrcDict()
+        self.monitoring = ircutils.IrcDict()
 
     def isChannel(self, s):
         """Helper function to check whether a given string is a channel on
@@ -965,7 +966,8 @@ class Irc(IrcCommandDispatcher):
         elif self.sasl_username and self.sasl_password:
             self.sasl = 'plain'
 
-        for cap in ('account-notify', 'extended-join', 'multi-prefix'):
+        for cap in ('account-notify', 'extended-join', 'multi-prefix',
+                'metadata-notify', 'account-tag'):
             self.queueMsg(ircmsgs.IrcMsg(command='CAP', args=('REQ', cap)))
 
         if self.sasl:
@@ -1041,6 +1043,38 @@ class Irc(IrcCommandDispatcher):
                         command='CAP',
                         args=('END',)))
 
+    def monitor(self, targets):
+        """Increment a counter of how many callbacks monitor each target;
+        and send a MONITOR + to the server if the target is not yet
+        monitored."""
+        if isinstance(targets, str):
+            targets = [targets]
+        not_yet_monitored = set()
+        for target in targets:
+            if target in self.monitoring:
+                self.monitoring[target] += 1
+            else:
+                not_yet_monitored.add(target)
+                self.monitoring[target] = 1
+        if not_yet_monitored:
+            self.queueMsg(ircmsgs.monitor('+', not_yet_monitored))
+        return not_yet_monitored
+
+    def unmonitor(self, targets):
+        """Decrements a counter of how many callbacks monitor each target;
+        and send a MONITOR - to the server if the counter drops to 0."""
+        if isinstance(targets, str):
+            targets = [targets]
+        should_be_unmonitored = set()
+        for target in targets:
+            self.monitoring[target] -= 1
+            if self.monitoring[target] == 0:
+                del self.monitoring[target]
+                should_be_unmonitored.add(target)
+        if should_be_unmonitored:
+            self.queueMsg(ircmsgs.monitor('-', should_be_unmonitored))
+        return should_be_unmonitored
+
     def do903(self, msg):
         log.info('%s: SASL authentication successful', self.network)
         self.queueMsg(ircmsgs.IrcMsg(command='CAP', args=('END',)))
diff --git a/src/ircmsgs.py b/src/ircmsgs.py
index 54ab272b3..45bf3104b 100644
--- a/src/ircmsgs.py
+++ b/src/ircmsgs.py
@@ -50,6 +50,37 @@ from .utils.iter import all
 class MalformedIrcMsg(ValueError):
     pass
 
+# http://ircv3.net/specs/core/message-tags-3.2.html#escaping-values
+SERVER_TAG_ESCAPE = [
+    ('\\', '\\\\'), # \ -> \\
+    (' ', r'\s'),
+    (';', r'\:'),
+    ('\r', r'\r'),
+    ('\n', r'\n'),
+    ]
+escape_server_tag_value = utils.str.MultipleReplacer(
+        dict(SERVER_TAG_ESCAPE))
+unescape_server_tag_value = utils.str.MultipleReplacer(
+        dict(map(lambda x:(x[1],x[0]), SERVER_TAG_ESCAPE)))
+
+def parse_server_tags(s):
+    server_tags = {}
+    for tag in s.split(';'):
+        if '=' not in tag:
+            server_tags[tag] = None
+        else:
+            (key, value) = tag.split('=', 1)
+            server_tags[key] = unescape_server_tag_value(value)
+    return server_tags
+def format_server_tags(server_tags):
+    parts = []
+    for (key, value) in server_tags.items():
+        if value is None:
+            parts.append(key)
+        else:
+            parts.append('%s=%s' % (key, escape_server_tag_value(value)))
+    return '@' + ';'.join(parts)
+
 class IrcMsg(object):
     """Class to represent an IRC message.
 
@@ -81,7 +112,8 @@ class IrcMsg(object):
     # data.  Goodbye, __slots__.
     # On second thought, let's use methods for tagging.
     __slots__ = ('args', 'command', 'host', 'nick', 'prefix', 'user',
-                 '_hash', '_str', '_repr', '_len', 'tags', 'reply_env')
+                 '_hash', '_str', '_repr', '_len', 'tags', 'reply_env',
+                 'server_tags')
     def __init__(self, s='', command='', args=(), prefix='', msg=None,
             reply_env=None):
         assert not (msg and s), 'IrcMsg.__init__ cannot accept both s and msg'
@@ -99,6 +131,11 @@ class IrcMsg(object):
                 if not s.endswith('\n'):
                     s += '\n'
                 self._str = s
+                if s[0] == '@':
+                    (server_tags, s) = s.split(' ', 1)
+                    self.server_tags = parse_server_tags(server_tags[1:])
+                else:
+                    self.server_tags = {}
                 if s[0] == ':':
                     self.prefix, s = s[1:].split(None, 1)
                 else:
@@ -818,6 +855,19 @@ def ison(nick, prefix='', msg=None):
         prefix = msg.prefix
     return IrcMsg(prefix=prefix, command='ISON', args=(nick,), msg=msg)
 
+def monitor(subcommand, nicks=None, prefix='', msg=None):
+    if conf.supybot.protocols.irc.strictRfc():
+        assert isNick(nick), repr(nick)
+        assert subcommand in '+-CLS'
+        if subcommand in 'CLS':
+            assert nicks is None
+    if msg and not prefix:
+        prefix = msg.prefix
+    if not isinstance(nicks, str):
+        nicks = ','.join(nicks)
+    return IrcMsg(prefix=prefix, command='MONITOR', args=(subcommand, nicks),
+            msg=msg)
+
 def error(s, msg=None):
     return IrcMsg(command='ERROR', args=(s,), msg=msg)
 
diff --git a/test/test_irclib.py b/test/test_irclib.py
index bb85f33fa..034ec725c 100644
--- a/test/test_irclib.py
+++ b/test/test_irclib.py
@@ -391,6 +391,10 @@ class IrcTestCase(SupyTestCase):
         m = self.irc.takeMsg()
         self.failUnless(m.command == 'CAP', 'Expected CAP, got %r.' % m)
         m = self.irc.takeMsg()
+        self.failUnless(m.command == 'CAP', 'Expected CAP, got %r.' % m)
+        m = self.irc.takeMsg()
+        self.failUnless(m.command == 'CAP', 'Expected CAP, got %r.' % m)
+        m = self.irc.takeMsg()
         self.failUnless(m.command == 'USER', 'Expected USER, got %r.' % m)
 
     def testPingResponse(self):
@@ -492,6 +496,8 @@ class IrcCallbackTestCase(SupyTestCase):
                 ircmsgs.IrcMsg(command='CAP', args=('REQ', 'account-notify')),
                 ircmsgs.IrcMsg(command='CAP', args=('REQ', 'extended-join')),
                 ircmsgs.IrcMsg(command='CAP', args=('REQ', 'multi-prefix')),
+                ircmsgs.IrcMsg(command='CAP', args=('REQ', 'metadata-notify')),
+                ircmsgs.IrcMsg(command='CAP', args=('REQ', 'account-tag')),
                 ircmsgs.IrcMsg(command='CAP', args=('END',)),
                 ircmsgs.user('limnoria', user)
             ]
diff --git a/test/test_ircmsgs.py b/test/test_ircmsgs.py
index 24960f500..583d0896a 100644
--- a/test/test_ircmsgs.py
+++ b/test/test_ircmsgs.py
@@ -128,6 +128,19 @@ class IrcMsgTestCase(SupyTestCase):
         m.tag('repliedTo', 12)
         self.assertEqual(m.repliedTo, 12)
 
+    def testServerTags(self):
+        s = '@aaa=b\\:bb;ccc;example.com/ddd=ee\\\\se ' \
+            ':nick!ident@host.com PRIVMSG me :Hello'
+        m = ircmsgs.IrcMsg(s)
+        self.assertEqual(m.server_tags, {
+            'aaa': 'b;bb',
+            'ccc': None,
+            'example.com/ddd': 'ee\\se'})
+        self.assertEqual(m.prefix, 'nick!ident@host.com')
+        self.assertEqual(m.command, 'PRIVMSG')
+        self.assertEqual(m.args, ('me', 'Hello'))
+        self.assertEqual(str(m), s + '\n')
+
 class FunctionsTestCase(SupyTestCase):
     def testIsAction(self):
         L = [':jemfinch!~jfincher@ts26-2.homenet.ohio-state.edu PRIVMSG'