diff --git a/gittip/networks/twitter.py b/gittip/networks/twitter.py
new file mode 100644
index 0000000000..ef2c03e128
--- /dev/null
+++ b/gittip/networks/twitter.py
@@ -0,0 +1,95 @@
+import requests
+from aspen import json, log, Response
+from aspen.website import Website
+from aspen.utils import typecheck
+from gittip import db, networks
+
+
+def upsert(user_info):
+    return networks.upsert( 'twitter'
+                          , user_info['id']
+                          , user_info['screen_name']
+                          , user_info
+                           )
+
+
+def oauth_url(website, action, then=u""):
+    """Given a website object and a string, return a URL string.
+
+    `action' is one of 'opt-in', 'lock' and 'unlock'
+
+    `then' is either a twitter username or an URL starting with '/'. It's
+        where we'll send the user after we get the redirect back from
+        GitHub.
+
+    """
+    typecheck(website, Website, action, unicode, then, unicode)
+    assert action in [u'opt-in', u'lock', u'unlock']
+    url = u"https://twitter.com/login/oauth/authorize?consumer_key=%s&redirect_uri=%s"
+    url %= (website.twitter_consumer_key, website.twitter_callback)
+
+    # Pack action,then into data and base64-encode. Querystring isn't
+    # available because it's consumed by the initial GitHub request.
+
+    data = u'%s,%s' % (action, then)
+    data = data.encode('UTF-8').encode('base64').decode('US-ASCII')
+    url += u'?data=%s' % data
+    return url
+
+
+def oauth_dance(website, qs):
+    """Given a querystring, return a dict of user_info.
+
+    The querystring should be the querystring that we get from GitHub when
+    we send the user to the return value of oauth_url above.
+
+    See also:
+
+        http://developer.twitter.com/v3/oauth/
+
+    """
+
+    log("Doing an OAuth dance with Github.")
+
+    if 'error' in qs:
+        raise Response(500, str(qs['error']))
+
+    data = { 'code': qs['code'].encode('US-ASCII')
+           , 'client_id': website.twitter_client_id
+           , 'client_secret': website.twitter_client_secret
+            }
+    r = requests.post("https://twitter.com/login/oauth/access_token", data=data)
+    assert r.status_code == 200, (r.status_code, r.text)
+
+    back = dict([pair.split('=') for pair in r.text.split('&')]) # XXX
+    if 'error' in back:
+        raise Response(400, back['error'].encode('utf-8'))
+    assert back.get('token_type', '') == 'bearer', back
+    access_token = back['access_token']
+
+    r = requests.get( "https://api.twitter.com/user"
+                    , headers={'Authorization': 'token %s' % access_token}
+                     )
+    assert r.status_code == 200, (r.status_code, r.text)
+    user_info = json.loads(r.text)
+    log("Done with OAuth dance with Github for %s (%s)."
+        % (user_info['login'], user_info['id']))
+
+    return user_info
+
+
+def resolve(screen_name):
+    """Given str, return a participant_id.
+    """
+    FETCH = """\
+
+        SELECT participant_id
+          FROM social_network_users
+         WHERE network='twitter'
+           AND user_info -> 'screen_namec' = %s
+
+    """ # XXX Uniqueness constraint on screen_name?
+    rec = db.fetchone(FETCH, (screen_name,))
+    if rec is None:
+        raise Exception("Twitter user %s has no participant." % (screen_name))
+    return rec['participant_id']
diff --git a/templates/participant.html b/templates/participant.html
index 040bf4f0e5..d9b82bf27e 100644
--- a/templates/participant.html
+++ b/templates/participant.html
@@ -14,7 +14,7 @@ <h2>Your weekly {{ tip_or_pledge }} to {{ username }} is:</h2>
 
             <div id="tips">
                 {% for amount in AMOUNTS %}
-                <button amount="{{ amount }}" tippee="{{ username }}"
+                <button amount="{{ amount }}" tippee="{{ participant_id }}"
                     class="tip{{ ' selected' if amount == my_tip else '' }}">${{ amount }}</button>
                 {% end %}
                 {% if my_tip not in AMOUNTS %}
diff --git a/www/%participant_id/tip.json b/www/%participant_id/tip.json
index 0d0c6857e4..0ff683482d 100644
--- a/www/%participant_id/tip.json
+++ b/www/%participant_id/tip.json
@@ -4,7 +4,6 @@ import decimal
 
 from aspen import Response
 from gittip import AMOUNTS, db
-from gittip.networks import github
 
 
 # ========================================================================== ^L
@@ -14,14 +13,11 @@ if not user.ANON:
 
     # Get tipper and tippee.
     # ======================
+    # XXX We could/should enforce that tips cannot be pledged at all to locked
+    # accounts.
 
     tipper = user.id
-    if 'participant_id' in path:    # gittip
-        tippee = path['participant_id']
-    elif 'login' in path:           # github
-        tippee = github.resolve(path['login'])
-    else:
-        raise Response(400, "can't find tippee")
+    tippee = path['participant_id']
 
 
     # Get and maybe set amount.
diff --git a/www/on/github/%login/index.html b/www/on/github/%login/index.html
index 8273300704..995a12c31f 100644
--- a/www/on/github/%login/index.html
+++ b/www/on/github/%login/index.html
@@ -51,7 +51,7 @@
     can_tip = False
 
 tip_or_pledge = "pledge"
-nbackers = get_number_of_backers(username)
+nbackers = get_number_of_backers(participant_id)
 
 # ========================================================================== ^L
 {% extends templates/participant.html %}
diff --git a/www/on/twitter/%screen_name/index.html b/www/on/twitter/%screen_name/index.html
new file mode 100644
index 0000000000..e814db4ccc
--- /dev/null
+++ b/www/on/twitter/%screen_name/index.html
@@ -0,0 +1,118 @@
+"""Twitter user page on Gittip.
+"""
+import decimal
+
+import requests
+from aspen import json, Response
+from gittip import AMOUNTS, CARDINALS, db, get_tip, get_number_of_backers
+from gittip.networks import twitter
+
+
+# ========================================================================== ^L
+
+# Try to load from Twitter.
+# =========================
+
+url = "https://api.twitter.com/1/users/show.json?screen_name=%s"
+userinfo = requests.get(url % path['screen_name'])
+if userinfo.status_code != 200:
+    raise Response(404)
+userinfo = json.loads(userinfo.text)
+
+
+# Try to load from Gittip.
+# ========================
+
+participant = False
+username = userinfo['screen_name']
+name = userinfo.get('name')
+if not name:
+    name = username
+userinfo['html_url'] = "https://twitter.com/%s" % username
+
+participant_id, is_claimed, is_locked, balance = twitter.upsert(userinfo)
+can_tip = not is_locked
+lock_action = "unlock" if is_locked else "lock"
+if is_claimed:
+    request.redirect('/%s/' % participant_id)
+
+if not user.ANON:
+    my_tip = get_tip(user.id, participant_id)
+
+tip_or_pledge = "pledge"
+nbackers = get_number_of_backers(participant_id)
+
+# ========================================================================== ^L
+{% extends templates/participant.html %}
+
+{% block their_voice %}
+  {% if is_locked %}
+
+    <h2 class="first"><b>{{ username }}</b> has opted out of Gittip.</h2>
+
+    <p>If you are <a href="{{ userinfo.get('html_url', '') }}">{{ username }}</a>
+    on Twitter, you can unlock your account to allow people to
+    pledge tips to you on Gittip. We never collect any money on your behalf
+    until you explicitly opt in.</p>
+
+    <a href="{{ twitter.oauth_url(website, u'unlock', username) }}"
+        ><button>Unlock</button></a>
+
+  {% else %}
+    <script>
+        $(document).ready(Gittip.initTipButtons);
+    </script>
+
+    <h2 class="first"><b>{{ name }}</b> has not joined Gittip.</h2>
+
+    {% if user.ANON %}
+    <ul id="accounts">
+        <li>
+            <img src="{{ userinfo.get('avatar_url', '/assets/%s/no-avatar.png' % __version__) }}" />
+            Are you <a href="{{ userinfo['html_url'] }}">{{ userinfo['screen_name'] }}</a> from Twitter?<br />
+            <a href="{{ twitter.oauth_url(website, u'opt-in', username) }}">Click here</a> to opt in to Gittip.
+        </li>
+    </ul>
+    {% else %}
+    <ul id="accounts">
+        <li>
+            <img src="{{ userinfo.get('avatar_url', '/assets/%s/no-avatar.png' % __version__) }}" />
+            Are you <a href="{{ userinfo['html_url'] }}">{{ userinfo['screen_name'] }}</a> from Twitter?<br />
+            You&rsquo;ll have to <a href="/sign-out.html">sign out</a> and sign back in to claim this account.
+        </li>
+    </ul>
+    {% end %}
+
+
+    {% if nbackers == 0 %}
+    {% elif nbackers == 1 %}
+    <h3>There is one person ready to give.</h3>
+    {% elif nbackers < 10 %}
+    <h3>There are {{ CARDINALS[nbackers] }} people ready to give.</h3>
+    {% else %}
+    <h3>There are {{ nbackers }} people ready to give.</h3>
+    {% end %}
+
+
+    {% if not user.ANON %}
+
+    <p>{{ 'But we' if nbackers > 0 else 'We' }} will never collect money on
+    behalf of {{ username }} until they ask us to.</p>
+
+    {% else %}
+
+    <p>{{ 'But we' if nbackers > 0 else 'We' }} will never collect money on
+    your behalf until you ask us to.</p>
+
+    <h3>Don&rsquo;t like what you see?</h3>
+
+    <p>If you are {{ username }} you can explicitly opt out of Gittip by
+    locking this account. We don&rsquo;t allow new pledges to locked
+    accounts.</p>
+
+    <a href="{{ twitter.oauth_url(website, u'lock', username) }}"
+        ><button>Lock</button></a>
+
+    {% end %}
+    {% end %}
+{% end %}