diff --git a/IRCBuffer.py b/IRCBuffer.py
index 6e689d30..619f9061 100644
--- a/IRCBuffer.py
+++ b/IRCBuffer.py
@@ -1,4 +1,5 @@
 import re
+import Utils
 
 class BufferLine(object):
     def __init__(self, sender, message, action, from_self):
@@ -28,7 +29,7 @@ class Buffer(object):
     def find(self, pattern, **kwargs):
         from_self = kwargs.get("from_self", True)
         for_user = kwargs.get("for_user", "")
-        for_user = for_user.lower() if for_user else None
+        for_user = Utils.irc_lower(for_user) if for_user else None
         not_pattern = kwargs.get("not_pattern", None)
         for line in self.lines:
             if line.from_self and not from_self:
@@ -36,7 +37,7 @@ class Buffer(object):
             elif re.search(pattern, line.message):
                 if not_pattern and re.search(not_pattern, line.message):
                     continue
-                if for_user and not line.sender.lower() == for_user:
+                if for_user and not Utils.irc_lower(line.sender) == for_user:
                     continue
                 return line
     def skip_next(self):
diff --git a/IRCChannel.py b/IRCChannel.py
index 0dfd6884..00407772 100644
--- a/IRCChannel.py
+++ b/IRCChannel.py
@@ -1,9 +1,9 @@
 import uuid
-import IRCBuffer
+import IRCBuffer, Utils
 
 class Channel(object):
     def __init__(self, name, id, server, bot):
-        self.name = name.lower()
+        self.name = Utils.irc_lower(name)
         self.id = id
         self.server = server
         self.bot = bot
diff --git a/IRCLineHandler.py b/IRCLineHandler.py
index 4a19082c..d7d47f54 100644
--- a/IRCLineHandler.py
+++ b/IRCLineHandler.py
@@ -5,6 +5,7 @@ RE_PREFIXES = re.compile(r"\bPREFIX=\((\w+)\)(\W+)(?:\b|$)")
 RE_CHANMODES = re.compile(
     r"\bCHANMODES=(\w*),(\w*),(\w*),(\w*)(?:\b|$)")
 RE_CHANTYPES = re.compile(r"\bCHANTYPES=(\W+)(?:\b|$)")
+RE_CASEMAPPING = re.compile(r"\bCASEMAPPING=(\S+)")
 RE_MODES = re.compile(r"[-+]\w+")
 
 CAPABILITIES = {"multi-prefix", "chghost", "invite-notify", "account-tag",
@@ -136,6 +137,11 @@ class LineHandler(object):
         match = re.search(RE_CHANTYPES, isupport_line)
         if match:
             event["server"].channel_types = list(match.group(1))
+
+        match = re.search(RE_CASEMAPPING, isupport_line)
+        if match:
+            event["server"].case_mapping = match.group(1)
+
         self.events.on("received.numeric.005").call(
             isupport=isupport_line, server=event["server"])
 
@@ -554,10 +560,11 @@ class LineHandler(object):
 
     # we need a registered nickname for this channel
     def handle_477(self, event):
-        if event["args"][1].lower() in event["server"].attempted_join:
+        channel_name = Utils.irc_lower(event["args"][1])
+        if channel_name in event["server"].attempted_join:
             self.bot.add_timer("rejoin", 5,
                 channel_name=event["args"][1],
-                key=event["server"].attempted_join[event["args"][1].lower()],
+                key=event["server"].attempted_join[channel_name],
                 server_id=event["server"].id)
 
     # someone's been kicked from a channel
diff --git a/IRCServer.py b/IRCServer.py
index a1e3a489..8b674711 100644
--- a/IRCServer.py
+++ b/IRCServer.py
@@ -47,6 +47,7 @@ class Server(object):
             {"@": "o", "+": "v"})
         self.channel_modes = []
         self.channel_types = []
+        self.case_mapping = "rfc1459"
 
         self.last_read = time.monotonic()
         self.last_send = None
@@ -130,9 +131,9 @@ class Server(object):
 
     def set_own_nickname(self, nickname):
         self.nickname = nickname
-        self.nickname_lower = nickname.lower()
+        self.nickname_lower = Utils.irc_lower(nickname)
     def is_own_nickname(self, nickname):
-        return nickname.lower() == self.nickname_lower
+        return Utils.irc_equals(nickname, self.nickname)
 
     def add_own_mode(self, mode, arg=None):
         self.own_modes[mode] = arg
@@ -145,7 +146,7 @@ class Server(object):
             self.add_own_mode(mode, arg)
 
     def has_user(self, nickname):
-        return nickname.lower() in self.users
+        return Utils.irc_lower(nickname) in self.users
     def get_user(self, nickname):
         if not self.has_user(nickname):
             user_id = self.get_user_id(nickname)
@@ -154,7 +155,7 @@ class Server(object):
                 user=new_user, server=self)
             self.users[new_user.nickname_lower] = new_user
             self.new_users.add(new_user)
-        return self.users[nickname.lower()]
+        return self.users[Utils.irc_lower(nickname)]
     def get_user_id(self, nickname):
         self.bot.database.users.add(self.id, nickname)
         return self.bot.database.users.get_id(self.id, nickname)
@@ -164,12 +165,12 @@ class Server(object):
             channel.remove_user(user)
 
     def change_user_nickname(self, old_nickname, new_nickname):
-        user = self.users.pop(old_nickname.lower())
+        user = self.users.pop(Utils.irc_lower(old_nickname))
         user._id = self.get_user_id(new_nickname)
-        self.users[new_nickname.lower()] = user
+        self.users[Utils.irc_lower(new_nickname)] = user
     def has_channel(self, channel_name):
-        return channel_name[0] in self.channel_types and channel_name.lower(
-            ) in self.channels
+        return channel_name[0] in self.channel_types and Utils.irc_lower(
+            channel_name) in self.channels
     def get_channel(self, channel_name):
         if not self.has_channel(channel_name):
             channel_id = self.get_channel_id(channel_name)
@@ -178,7 +179,7 @@ class Server(object):
             self.events.on("new").on("channel").call(
                 channel=new_channel, server=self)
             self.channels[new_channel.name] = new_channel
-        return self.channels[channel_name.lower()]
+        return self.channels[Utils.irc_lower(channel_name)]
     def get_channel_id(self, channel_name):
         self.bot.database.channels.add(self.id, channel_name)
         return self.bot.database.channels.get_id(self.id, channel_name)
diff --git a/IRCUser.py b/IRCUser.py
index 1bb7ad13..d336ecf1 100644
--- a/IRCUser.py
+++ b/IRCUser.py
@@ -1,5 +1,5 @@
 import uuid
-import IRCBuffer
+import IRCBuffer, Utils
 
 class User(object):
     def __init__(self, nickname, id, server, bot):
@@ -31,7 +31,7 @@ class User(object):
 
     def set_nickname(self, nickname):
         self.nickname = nickname
-        self.nickname_lower = nickname.lower()
+        self.nickname_lower = Utils.irc_lower(nickname)
         self.name = self.nickname_lower
     def join_channel(self, channel):
         self.channels.add(channel)
diff --git a/Utils.py b/Utils.py
index 0aa407d4..ac39825c 100644
--- a/Utils.py
+++ b/Utils.py
@@ -1,10 +1,14 @@
 import json, re, traceback, urllib.request, urllib.parse, urllib.error, ssl
+import string
 import bs4
 
 USER_AGENT = ("Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 "
     "(KHTML, like Gecko) Chrome/49.0.2623.87 Safari/537.36")
 REGEX_HTTP = re.compile("https?://", re.I)
 
+RFC1459_UPPER = r'\[]~'
+RFC1459_UPPER = r'|{}^'
+
 def remove_colon(s):
     if s.startswith(":"):
         s = s[1:]
@@ -13,6 +17,21 @@ def remove_colon(s):
 def arbitrary(s, n):
     return remove_colon(" ".join(s[n:]))
 
+def _rfc1459_lower(s):
+    for upper, lower in zip(RFC1459_UPPER, RFC1459_LOWER):
+        s = s.replace(upper, lower)
+    return s.lower()
+def irc_lower(server, s):
+    if server.case_mapping == "ascii":
+        return s.lower()
+    elif server.case_mapping == "rfc1459":
+        return _rfc1459_lower(s)
+    else:
+        raise ValueError("unknown casemapping '%s'" % server.case_mapping)
+
+def irc_equals(server, s1, s2):
+    return irc_lower(server, s1) == irc_lower(server, s2)
+
 class IRCHostmask(object):
     def __init__(self, nickname, username, hostname, hostmask):
         self.nickname = nickname