diff --git a/sequence.ml b/sequence.ml
index 58100c5..68b6e8a 100644
--- a/sequence.ml
+++ b/sequence.ml
@@ -30,11 +30,19 @@ let filter p seq =
   let seq_fun' k = seq.seq_fun (fun x -> if p x then k x) in
   { seq_fun=seq_fun'; }
 
-(** Concatenate two sequences *)
-let concat s1 s2 =
+(** Append two sequences *)
+let append s1 s2 =
   let seq_fun k = s1.seq_fun k; s2.seq_fun k in
   { seq_fun; }
 
+(** Concatenate a sequence of sequences into one sequence *)
+let concat s =
+  let seq_fun k =
+    (* function that is called on every sub-sequence *)
+    let k_seq seq = iter k seq in
+    s.seq_fun k_seq
+  in { seq_fun; }
+
 (** Take at most [n] elements from the sequence *)
 let take n seq =
   let count = ref 0 in
diff --git a/sequence.mli b/sequence.mli
index b21562c..4445b2f 100644
--- a/sequence.mli
+++ b/sequence.mli
@@ -23,8 +23,11 @@ val map : ('a -> 'b) -> 'a t -> 'b t
 val filter : ('a -> bool) -> 'a t -> 'a t
   (** Filter on elements of the sequence *)
 
-val concat : 'a t -> 'a t -> 'a t
-  (** Concatenate two sequences *)
+val append : 'a t -> 'a t -> 'a t
+  (** Append two sequences *)
+
+val concat : 'a t t -> 'a t
+  (** Concatenate a sequence of sequences into one sequence *)
 
 val take : int -> 'a t -> 'a t
   (** Take at most [n] elements from the sequence *)