diff --git a/src/core/CCString.ml b/src/core/CCString.ml
index 260d9d69..ec87f351 100644
--- a/src/core/CCString.ml
+++ b/src/core/CCString.ml
@@ -585,6 +585,24 @@ let take n s =
   else
     s
 
+let take_while f s =
+  let i = ref 0 in
+  while !i < String.length s && f (String.unsafe_get s !i) do
+    incr i
+  done;
+  String.sub s 0 !i
+
+let rtake_while f s =
+  let s_len_pred = String.length s - 1 in
+  let i = ref s_len_pred in
+  while !i >= 0 && f (String.unsafe_get s !i) do
+    decr i
+  done;
+  if !i < s_len_pred then
+    String.sub s (!i + 1) (s_len_pred - !i)
+  else
+    ""
+
 let drop n s =
   if n < String.length s then
     String.sub s n (String.length s - n)
diff --git a/src/core/CCString.mli b/src/core/CCString.mli
index 0e5e7ba0..9d2a66ee 100644
--- a/src/core/CCString.mli
+++ b/src/core/CCString.mli
@@ -182,6 +182,16 @@ val take : int -> string -> string
 (** [take n s] keeps only the [n] first chars of [s].
     @since 0.17 *)
 
+val take_while : (char -> bool) -> string -> string
+(** [take_while f s] keeps only the longest prefix [t] of [s] such that every
+    character [c] in [t] satisfies [f c].
+    @since 3.16 *)
+
+val rtake_while : (char -> bool) -> string -> string
+(** [rtake_while f s] keeps only the longest suffix [t] of [s] such that every
+    character [c] in [t] satisfies [f c].
+    @since 3.16 *)
+
 val drop : int -> string -> string
 (** [drop n s] removes the [n] first chars of [s].
     @since 0.17 *)
diff --git a/src/core/CCStringLabels.mli b/src/core/CCStringLabels.mli
index 318e8237..0bd3f1d7 100644
--- a/src/core/CCStringLabels.mli
+++ b/src/core/CCStringLabels.mli
@@ -193,6 +193,16 @@ val take : int -> string -> string
 (** [take n s] keeps only the [n] first chars of [s].
     @since 0.17 *)
 
+val take_while : f:(char -> bool) -> string -> string
+(** [take_while ~f s] keeps only the longest prefix [t] of [s] such that every
+    character [c] in [t] satisfies [f c].
+    @since 3.16 *)
+
+val rtake_while : f:(char -> bool) -> string -> string
+(** [rtake_while ~f s] keeps only the longest suffix [t] of [s] such that every
+    character [c] in [t] satisfies [f c].
+    @since 3.16 *)
+
 val drop : int -> string -> string
 (** [drop n s] removes the [n] first chars of [s].
     @since 0.17 *)
diff --git a/tests/core/t_string.ml b/tests/core/t_string.ml
index 4db9bea5..47f1f00b 100644
--- a/tests/core/t_string.ml
+++ b/tests/core/t_string.ml
@@ -280,6 +280,23 @@ eq ~printer:CCFun.id "" (unlines []);;
 eq ~printer:CCFun.id "ab\nc\n" (unlines [ "ab"; "c" ]);;
 q Q.printable_string (fun s -> trim (unlines (lines s)) = trim s);;
 q Q.printable_string (fun s -> trim (unlines_gen (lines_gen s)) = trim s);;
+eq ~printer:CCFun.id "" (take_while (Char.equal 'c') "heloo_cc");;
+eq ~printer:CCFun.id "" (take_while (Char.equal 'c') "");;
+eq ~printer:CCFun.id "c" (take_while (Char.equal 'c') "c");;
+eq ~printer:CCFun.id "ccc" (take_while (Char.equal 'c') "cccujsuy");;
+
+eq ~printer:CCFun.id "THIS"
+  (take_while (fun c -> Char.code c < 91) "THISisNotWHAtIwANTED")
+;;
+
+eq ~printer:CCFun.id "cc" (rtake_while (Char.equal 'c') "heloo_cc");;
+eq ~printer:CCFun.id "" (rtake_while (Char.equal 'c') "");;
+eq ~printer:CCFun.id "c" (rtake_while (Char.equal 'c') "c");;
+eq ~printer:CCFun.id "" (rtake_while (Char.equal 'c') "cccujsuy");;
+
+eq ~printer:CCFun.id "ANTED"
+  (rtake_while (fun c -> Char.code c < 91) "THISisNotWHAtIwANTED")
+;;
 
 q
   Q.(small_list small_string)