diff --git a/README.md b/README.md
index 8080b12..1e986b4 100644
--- a/README.md
+++ b/README.md
@@ -41,7 +41,7 @@ For the first first version of Flamingo, to be integrated into Bob the Builder (
 - [x] Vector indexing getters (i.e. `v[0]`).
 - [x] Anonymous functions (lambda).
 - [x] Vector `.map` function.
-- [ ] Vector `.where` function.
+- [x] Vector `.where` function.
 - [ ] Vector slicing (i.e. `v[1:3]`).
 - [ ] Vector indexing setters.
 - [ ] Vector slicing setters.
diff --git a/flamingo/primitive_type_member.h b/flamingo/primitive_type_member.h
index 108c16b..3d80d3e 100644
--- a/flamingo/primitive_type_member.h
+++ b/flamingo/primitive_type_member.h
@@ -205,6 +205,67 @@ static int vec_map(flamingo_t* flamingo, flamingo_val_t* self, flamingo_arg_list
 	return 0;
 }
 
+static int vec_where(flamingo_t* flamingo, flamingo_val_t* self, flamingo_arg_list_t* args, flamingo_val_t** rv) {
+	assert(self->kind == FLAMINGO_VAL_KIND_VEC);
+
+	// Check our arguments.
+
+	if (args->count != 1) {
+		return error(flamingo, "'vec.where' expected 1 argument, got %zu", args->count);
+	}
+
+	flamingo_val_t* const fn = args->args[0];
+
+	if (fn->kind != FLAMINGO_VAL_KIND_FN) {
+		return error(flamingo, "'vec.where' expected 'fn' argument to be a function, got a %s", val_type_str(fn));
+	}
+
+	// Actually filter the vector.
+
+	flamingo_val_t* const vec = val_alloc();
+	vec->kind = FLAMINGO_VAL_KIND_VEC;
+	vec->vec.count = 0;
+	vec->vec.elems = NULL;
+
+	for (size_t i = 0; i < self->vec.count; i++) {
+		flamingo_val_t* const elem = self->vec.elems[i];
+		flamingo_val_t* const args[] = {elem};
+
+		flamingo_arg_list_t arg_list = {
+			.count = 1,
+			.args = (void*) args,
+		};
+
+		flamingo_val_t* keep = NULL;
+
+		if (call(flamingo, fn, NULL, &keep, &arg_list) < 0) {
+			val_free(vec);
+			return -1;
+		}
+
+		if (keep->kind != FLAMINGO_VAL_KIND_BOOL) {
+			val_free(keep);
+			val_free(vec);
+			return error(flamingo, "'vec.where' expected 'fn' to return a boolean, got a %s", val_type_str(keep));
+		}
+
+		if (!keep->boolean.boolean) {
+			val_free(keep);
+			continue;
+		}
+
+		val_free(keep);
+
+		vec->vec.elems = realloc(vec->vec.elems, ++vec->vec.count * sizeof *vec->vec.elems);
+		assert(vec->vec.elems != NULL);
+		vec->vec.elems[vec->vec.count - 1] = val_copy(elem);
+	}
+
+	*rv = vec;
+
+	return 0;
+}
+
 static int primitive_type_member_std(flamingo_t* flamingo) {
 #define ADD(type, key, cb)                                                               \
 	do {                                                                                  \
@@ -219,6 +280,7 @@ static int primitive_type_member_std(flamingo_t* flamingo) {
 
 	ADD(FLAMINGO_VAL_KIND_VEC, "len", vec_len);
 	ADD(FLAMINGO_VAL_KIND_VEC, "map", vec_map);
+	ADD(FLAMINGO_VAL_KIND_VEC, "where", vec_where);
 
 	return 0;
 }
diff --git a/tests/vec.fl b/tests/vec.fl
index ce216fa..9fc7e77 100644
--- a/tests/vec.fl
+++ b/tests/vec.fl
@@ -21,3 +21,18 @@ assert v[2] == 3
 # Mapping.
 
 assert [1, 2, 3].map(|x| 2 * x) == [2, 4, 6]
+
+# Filtering.
+
+assert [
+	"textfile.txt",
+	"main.c",
+	"image.png",
+	"image2.png",
+	"header.h",
+	"util.c",
+].where(|x| x.endswith(".c") || x.endswith(".h")) == [
+	"main.c",
+	"header.h",
+	"util.c"
+]