diff --git a/TODO.txt b/TODO.txt
index 77476d5..c5f8e5d 100644
--- a/TODO.txt
+++ b/TODO.txt
@@ -15,8 +15,6 @@ WISHLIST
 
 - automatic markdown bold/italic formatting
 
-- support WHOIS
-
 - support USERIP/KILL/KICK for ops
 
 - use CTCP chat to support irc-special characters in chat messages (colon, newline)
diff --git a/server.go b/server.go
index e3383a0..26f51a8 100644
--- a/server.go
+++ b/server.go
@@ -657,6 +657,35 @@ func (s *Server) handleJoinedCommand(command string, args []string) {
 
 		return
 
+	case "WHOIS":
+		if len(args) < 1 {
+			s.reply(errMoreArgs)
+			return
+		}
+
+		// WHOIS [target] nick[,nick2[,nick...]]
+		nicklist := args[0] // Assume WHOIS ${nick} only,
+		if len(args) >= 2 {
+			nicklist = args[1] // It was WHOIS ${target} ${nick} instead
+		}
+
+		for _, targetnick := range strings.Split(nicklist, ",") {
+			// tell the client something about it
+			// The protocol does ostensibly support wildcard WHOIS, but we don't (yet)
+			s.upstream.Users(func(u *map[string]libnmdc.UserInfo) error {
+				for nick, nickinfo := range *u {
+					if nick == targetnick {
+						s.reply(rplWhoisUser, nick, nickinfo.Description+" <"+nickinfo.ClientVersion+">")
+						if nickinfo.IsOperator {
+							s.reply(rplWhoisOperator, nick)
+						}
+					}
+				}
+				return nil
+			})
+			s.reply(rplEndOfWhois)
+		}
+
 	default:
 		s.reply(errUnknownCommand, command)
 	}
@@ -815,6 +844,13 @@ func (s *Server) reply(code replyCode, args ...string) {
 	case rplPong:
 		s.writeClient(fmt.Sprintf(":%s PONG %s %s", s.name, s.clientNick(), args[0]))
 
+	case rplWhoisUser:
+		s.writeClient(fmt.Sprintf(":%s 311 %s %s %s * :%s", s.name, args[0], args[0], args[0], args[1])) // caller should supply nick,description
+	case rplWhoisOperator:
+		s.writeClient(fmt.Sprintf(":%s 313 %s :is an IRC operator", s.name, args[0]))
+	case rplEndOfWhois:
+		s.writeClient(fmt.Sprintf(":%s 318 :End of WHOIS list", s.name))
+
 	case errMoreArgs:
 		s.writeClient(fmt.Sprintf(":%s 461 %s :Not enough params", s.name, s.clientNick()))
 	case errNoNick:
diff --git a/typedefs.go b/typedefs.go
index ad12382..c7c2c3c 100644
--- a/typedefs.go
+++ b/typedefs.go
@@ -56,6 +56,9 @@ const (
 	rplMOTD
 	rplEndOfMOTD
 	rplPong
+	rplWhoisUser
+	rplWhoisOperator
+	rplEndOfWhois
 	errMoreArgs
 	errNoNick
 	errInvalidNick