diff --git a/src/kike.c b/src/kike.c
index aea6612..08da922 100644
--- a/src/kike.c
+++ b/src/kike.c
@@ -803,6 +803,7 @@ enum
 	IRC_RPL_USERHOST              = 302,
 	IRC_RPL_UNAWAY                = 305,
 	IRC_RPL_NOWAWAY               = 306,
+	IRC_RPL_ENDOFWHO              = 315,
 	IRC_RPL_LIST                  = 322,
 	IRC_RPL_LISTEND               = 323,
 	IRC_RPL_CHANNELMODEIS         = 324,
@@ -813,6 +814,7 @@ enum
 	IRC_RPL_EXCEPTLIST            = 348,
 	IRC_RPL_ENDOFEXCEPTLIST       = 349,
 	IRC_RPL_VERSION               = 351,
+	IRC_RPL_WHOREPLY              = 352,
 	IRC_RPL_NAMREPLY              = 353,
 	IRC_RPL_ENDOFNAMES            = 366,
 	IRC_RPL_BANLIST               = 367,
@@ -868,6 +870,7 @@ static const char *g_default_replies[] =
 	[IRC_RPL_USERHOST] = ":%s",
 	[IRC_RPL_UNAWAY] = ":You are no longer marked as being away",
 	[IRC_RPL_NOWAWAY] = ":You have been marked as being away",
+	[IRC_RPL_ENDOFWHO] = "%s :End of WHO list",
 	[IRC_RPL_LIST] = "%s %d :%s",
 	[IRC_RPL_LISTEND] = ":End of LIST",
 	[IRC_RPL_CHANNELMODEIS] = "%s +%s",
@@ -878,6 +881,7 @@ static const char *g_default_replies[] =
 	[IRC_RPL_EXCEPTLIST] = "%s %s",
 	[IRC_RPL_ENDOFEXCEPTLIST] = "%s :End of channel exception list",
 	[IRC_RPL_VERSION] = "%s.%d %s :%s",
+	[IRC_RPL_WHOREPLY] = "%s %s %s %s %s %s :%d %s",
 	[IRC_RPL_NAMREPLY] = "%c %s :%s",
 	[IRC_RPL_ENDOFNAMES] = "%s :End of NAMES list",
 	[IRC_RPL_BANLIST] = "%s %s",
@@ -1445,6 +1449,109 @@ irc_handle_names (const struct irc_message *msg, struct client *c)
 	}
 }
 
+static void
+irc_send_rpl_whoreply (struct client *c, const struct channel *chan,
+	const struct client *target)
+{
+	struct str chars;
+	str_init (&chars);
+
+	str_append_c (&chars, target->away_message ? 'G' : 'H');
+	if (target->mode & IRC_USER_MODE_OPERATOR)
+		str_append_c (&chars, '*');
+
+	struct channel_user *user;
+	if (chan && (user = channel_get_user (chan, target)))
+	{
+		if (user->modes & IRC_CHAN_MODE_OPERATOR)
+			str_append_c (&chars, '@');
+		else if (user->modes & IRC_CHAN_MODE_VOICE)
+			str_append_c (&chars, '+');
+	}
+
+	irc_send_reply (c, IRC_RPL_WHOREPLY, chan ? chan->name : "*",
+		target->username, target->hostname, target->ctx->server_name,
+		target->nickname, chars.str, 0 /* hop count */, target->realname);
+	str_free (&chars);
+}
+
+static void
+irc_match_send_rpl_whoreply (struct client *c, struct client *target,
+	const char *mask)
+{
+	bool is_roommate = false;
+	struct str_map_iter iter;
+	str_map_iter_init (&iter, &c->ctx->channels);
+	struct channel *chan;
+	while ((chan = str_map_iter_next (&iter)))
+		if (channel_get_user (chan, target) && channel_get_user (chan, c))
+		{
+			is_roommate = true;
+			break;
+		}
+	if ((target->mode & IRC_USER_MODE_INVISIBLE) && !is_roommate)
+		return;
+
+	if (fnmatch (mask, target->hostname,    0)
+	 && fnmatch (mask, target->nickname,    0)
+	 && fnmatch (mask, target->realname,    0)
+	 && fnmatch (mask, c->ctx->server_name, 0))
+		return;
+
+	// Try to find a channel they're on that's visible to us
+	struct channel *user_chan = NULL;
+	str_map_iter_init (&iter, &c->ctx->channels);
+	while ((chan = str_map_iter_next (&iter)))
+		if (channel_get_user (chan, target)
+		 && (!(chan->modes & (IRC_CHAN_MODE_PRIVATE | IRC_CHAN_MODE_SECRET))
+			|| channel_get_user (chan, c)))
+		{
+			user_chan = chan;
+			break;
+		}
+	irc_send_rpl_whoreply (c, user_chan, target);
+}
+
+static void
+irc_handle_who (const struct irc_message *msg, struct client *c)
+{
+	bool only_ops = msg->params.len > 1 && !strcmp (msg->params.vector[1], "o");
+
+	const char *shown_mask = msg->params.vector[0], *used_mask;
+	if (!shown_mask)
+		used_mask = shown_mask = "*";
+	else if (!strcmp (shown_mask, "0"))
+		used_mask = "*";
+	else
+		used_mask = shown_mask;
+
+	struct channel *chan;
+	if ((chan = str_map_find (&c->ctx->channels, used_mask)))
+	{
+		bool on_chan = !!channel_get_user (chan, c);
+		if (on_chan || !(chan->modes & IRC_CHAN_MODE_SECRET))
+			for (struct channel_user *iter = chan->users;
+				iter; iter = iter->next)
+			{
+				struct client *target =
+					str_map_find (&c->ctx->users, iter->nickname);
+				if ((on_chan || !(target->mode & IRC_USER_MODE_INVISIBLE))
+				 && (!only_ops || (target->mode & IRC_USER_MODE_OPERATOR)))
+					irc_send_rpl_whoreply (c, chan, target);
+			}
+	}
+	else
+	{
+		struct str_map_iter iter;
+		str_map_iter_init (&iter, &c->ctx->users);
+		struct client *target;
+		while ((target = str_map_iter_next (&iter)))
+			if (!only_ops || (target->mode & IRC_USER_MODE_OPERATOR))
+				irc_match_send_rpl_whoreply (c, target, used_mask);
+	}
+	irc_send_reply (c, IRC_RPL_ENDOFWHO, shown_mask);
+}
+
 static void
 irc_send_rpl_topic (struct client *c, struct channel *chan)
 {
@@ -1686,6 +1793,7 @@ irc_register_handlers (struct server_context *ctx)
 		{ "TOPIC",    true,  irc_handle_topic    },
 		{ "LIST",     true,  irc_handle_list     },
 		{ "NAMES",    true,  irc_handle_names    },
+		{ "WHO",      true,  irc_handle_who      },
 	};
 
 	for (size_t i = 0; i < N_ELEMENTS (message_handlers); i++)