diff --git a/irc/client.go b/irc/client.go
index 7047f164..07d4bc87 100644
--- a/irc/client.go
+++ b/irc/client.go
@@ -225,6 +225,7 @@ func (client *Client) ChangeNickname(nickname string) {
 	// Make reply before changing nick to capture original source id.
 	reply := RplNick(client, nickname)
 	client.server.clients.Remove(client)
+	client.server.whoWas.Append(client)
 	client.nick = nickname
 	client.server.clients.Add(client)
 	for friend := range client.Friends() {
@@ -242,8 +243,8 @@ func (client *Client) Quit(message string) {
 	}
 
 	client.Reply(RplError("connection closed"))
-
 	client.hasQuit = true
+	client.server.whoWas.Append(client)
 	friends := client.Friends()
 	friends.Remove(client)
 	client.destroy()
diff --git a/irc/reply.go b/irc/reply.go
index a32a5765..5f538df5 100644
--- a/irc/reply.go
+++ b/irc/reply.go
@@ -394,9 +394,10 @@ func (target *Client) RplTime() {
 		"%s :%s", target.server.name, time.Now().Format(time.RFC1123))
 }
 
-func (target *Client) RplWhoWasUser(nickname, username, hostname, realname string) {
+func (target *Client) RplWhoWasUser(whoWas *WhoWas) {
 	target.NumericReply(RPL_WHOWASUSER,
-		"%s %s %s * :%s", nickname, username, hostname, realname)
+		"%s %s %s * :%s",
+		whoWas.nickname, whoWas.username, whoWas.hostname, whoWas.realname)
 }
 
 func (target *Client) RplEndOfWhoWas(nickname string) {
diff --git a/irc/server.go b/irc/server.go
index 16ee7b11..53e476fd 100644
--- a/irc/server.go
+++ b/irc/server.go
@@ -30,6 +30,7 @@ type Server struct {
 	password  []byte
 	signals   chan os.Signal
 	timeout   chan *Client
+	whoWas    *WhoWasList
 }
 
 func NewServer(config *Config) *Server {
@@ -46,6 +47,7 @@ func NewServer(config *Config) *Server {
 		operators: config.Operators(),
 		signals:   make(chan os.Signal, 1),
 		timeout:   make(chan *Client, 16),
+		whoWas:    NewWhoWasList(100),
 	}
 
 	if config.Server.Password != "" {
@@ -846,8 +848,14 @@ func (msg *KillCommand) HandleServer(server *Server) {
 func (msg *WhoWasCommand) HandleServer(server *Server) {
 	client := msg.Client()
 	for _, nickname := range msg.nicknames {
-		// TODO implement nick history
-		client.ErrWasNoSuchNick(nickname)
+		results := server.whoWas.Find(nickname, msg.count)
+		if len(results) == 0 {
+			client.ErrWasNoSuchNick(nickname)
+		} else {
+			for _, whoWas := range results {
+				client.RplWhoWasUser(whoWas)
+			}
+		}
 		client.RplEndOfWhoWas(nickname)
 	}
 }
diff --git a/irc/whowas.go b/irc/whowas.go
new file mode 100644
index 00000000..008ed7f3
--- /dev/null
+++ b/irc/whowas.go
@@ -0,0 +1,73 @@
+package irc
+
+type WhoWasList struct {
+	buffer []*WhoWas
+	start  uint
+	end    uint
+}
+
+type WhoWas struct {
+	nickname string
+	username string
+	hostname string
+	realname string
+}
+
+func NewWhoWasList(size uint) *WhoWasList {
+	return &WhoWasList{
+		buffer: make([]*WhoWas, size),
+	}
+}
+
+func (list *WhoWasList) Append(client *Client) {
+	list.buffer[list.end] = &WhoWas{
+		nickname: client.Nick(),
+		username: client.username,
+		hostname: client.hostname,
+		realname: client.realname,
+	}
+	list.end = (list.end + 1) % uint(len(list.buffer))
+	if list.end == list.start {
+		list.start = (list.end + 1) % uint(len(list.buffer))
+	}
+}
+
+func (list *WhoWasList) Find(nickname string, limit int64) []*WhoWas {
+	results := make([]*WhoWas, 0)
+	for whoWas := range list.Each() {
+		if nickname != whoWas.nickname {
+			continue
+		}
+		results = append(results, whoWas)
+		if int64(len(results)) >= limit {
+			break
+		}
+	}
+	return results
+}
+
+func (list *WhoWasList) prev(index uint) uint {
+	index -= 1
+	if index < 0 {
+		index += uint(len(list.buffer))
+	}
+	return index
+}
+
+// Iterate the buffer in reverse.
+func (list *WhoWasList) Each() <-chan *WhoWas {
+	ch := make(chan *WhoWas)
+	go func() {
+		defer close(ch)
+		if list.start == list.end {
+			return
+		}
+		start := list.prev(list.end)
+		end := list.prev(list.start)
+		for start != end {
+			ch <- list.buffer[start]
+			start = list.prev(start)
+		}
+	}()
+	return ch
+}