diff --git a/compiler/builtins/src/std.rs b/compiler/builtins/src/std.rs
index a78af7e971..f934e83143 100644
--- a/compiler/builtins/src/std.rs
+++ b/compiler/builtins/src/std.rs
@@ -877,6 +877,19 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
         Box::new(list_type(int_type(flex(TVAR1)))),
     );
 
+    // joinMap : List before, (before -> List after) -> List after
+    {
+        let_tvars! { cvar, before, after }
+        add_top_level_function_type!(
+            Symbol::LIST_JOIN_MAP,
+            vec![
+                list_type(flex(before)),
+                closure(vec![flex(before)], cvar, Box::new(list_type(flex(after)))),
+            ],
+            Box::new(list_type(flex(after))),
+        );
+    }
+
     // map : List before, (before -> after) -> List after
     add_top_level_function_type!(
         Symbol::LIST_MAP,
diff --git a/compiler/can/src/builtins.rs b/compiler/can/src/builtins.rs
index d89fc247e7..f4a2b2de33 100644
--- a/compiler/can/src/builtins.rs
+++ b/compiler/can/src/builtins.rs
@@ -86,6 +86,7 @@ pub fn builtin_defs_map(symbol: Symbol, var_store: &mut VarStore) -> Option<Def>
         LIST_PRODUCT => list_product,
         LIST_PREPEND => list_prepend,
         LIST_JOIN => list_join,
+        LIST_JOIN_MAP => list_join_map,
         LIST_MAP => list_map,
         LIST_MAP2 => list_map2,
         LIST_MAP3 => list_map3,
@@ -2200,6 +2201,83 @@ fn list_walk_until(symbol: Symbol, var_store: &mut VarStore) -> Def {
     lowlevel_3(symbol, LowLevel::ListWalkUntil, var_store)
 }
 
+/// List.joinMap : List before, (before -> List after) -> List after
+fn list_join_map(symbol: Symbol, var_store: &mut VarStore) -> Def {
+    let before = var_store.fresh();
+    let list_before = var_store.fresh();
+    let after = var_store.fresh();
+    let list_after = var_store.fresh();
+    let before2list_after = var_store.fresh();
+    let t_concat_clos = var_store.fresh();
+    let mapper_lambda_set = var_store.fresh();
+
+    // \state, elem -> List.concat state (mapper elem)
+    let concat_clos = Closure(ClosureData {
+        function_type: t_concat_clos,
+        closure_type: var_store.fresh(),
+        closure_ext_var: var_store.fresh(),
+        return_type: list_after,
+        name: Symbol::LIST_JOIN_MAP_CONCAT,
+        recursive: Recursive::NotRecursive,
+        captured_symbols: vec![(Symbol::ARG_2, before2list_after)],
+        arguments: vec![
+            (list_after, no_region(Pattern::Identifier(Symbol::ARG_3))),
+            (before, no_region(Pattern::Identifier(Symbol::ARG_4))),
+        ],
+        loc_body: {
+            let mapper = Box::new((
+                before2list_after,
+                no_region(Var(Symbol::ARG_2)),
+                mapper_lambda_set,
+                list_after, // return type
+            ));
+            // (mapper elem)
+            let mapper_elem = Call(
+                mapper,
+                vec![(before, no_region(Var(Symbol::ARG_4)))],
+                CalledVia::Space,
+            );
+            Box::new(no_region(RunLowLevel {
+                op: LowLevel::ListConcat,
+                args: vec![(list_after, Var(Symbol::ARG_3)), (list_after, mapper_elem)],
+                ret_var: list_after,
+            }))
+        },
+    });
+
+    // List.joinMap = \input_list, mapper ->
+    //   List.walk [] input_list (\state, elem -> List.concat state (mapper elem))
+    let body = RunLowLevel {
+        op: LowLevel::ListWalk,
+        args: vec![
+            // input_list : List before
+            (list_before, Var(Symbol::ARG_1)),
+            // [] : List after
+            (
+                list_after,
+                List {
+                    elem_var: after,
+                    loc_elems: vec![],
+                },
+            ),
+            // \state, elem -> List.concat state (mapper elem)
+            (t_concat_clos, concat_clos),
+        ],
+        ret_var: list_after,
+    };
+
+    defn(
+        symbol,
+        vec![
+            (list_before, Symbol::ARG_1),
+            (before2list_after, Symbol::ARG_2),
+        ],
+        var_store,
+        body,
+        list_after,
+    )
+}
+
 // min :  List (Num a) -> Result (Num a) [ ListWasEmpty ]*
 fn list_min(symbol: Symbol, var_store: &mut VarStore) -> Def {
     let arg_var = var_store.fresh();
diff --git a/compiler/module/src/symbol.rs b/compiler/module/src/symbol.rs
index 36aa6e6675..22a3521b1b 100644
--- a/compiler/module/src/symbol.rs
+++ b/compiler/module/src/symbol.rs
@@ -1062,6 +1062,8 @@ define_builtins! {
         39 LIST_MAX_GT: "#maxGt"
         40 LIST_MAP4: "map4"
         41 LIST_DROP_FIRST: "dropFirst"
+        42 LIST_JOIN_MAP: "joinMap"
+        43 LIST_JOIN_MAP_CONCAT: "#joinMapConcat"
     }
     5 RESULT: "Result" => {
         0 RESULT_RESULT: "Result" imported // the Result.Result type alias
diff --git a/compiler/test_gen/src/gen_list.rs b/compiler/test_gen/src/gen_list.rs
index 81a86804bf..cfaaf122cb 100644
--- a/compiler/test_gen/src/gen_list.rs
+++ b/compiler/test_gen/src/gen_list.rs
@@ -2221,3 +2221,35 @@ fn empty_list_of_function_type() {
         RocStr
     );
 }
+
+#[test]
+fn list_join_map() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+            List.joinMap ["guava,apple,pear", "bailey,cyrus"] (\s -> Str.split s ",")
+            "#
+        ),
+        RocList::from_slice(&[
+            RocStr::from_slice("guava".as_bytes()),
+            RocStr::from_slice("apple".as_bytes()),
+            RocStr::from_slice("pear".as_bytes()),
+            RocStr::from_slice("bailey".as_bytes()),
+            RocStr::from_slice("cyrus".as_bytes()),
+        ]),
+        RocList<RocStr>
+    );
+}
+
+#[test]
+fn list_join_map_empty() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+            List.joinMap [] (\s -> Str.split s ",")
+            "#
+        ),
+        RocList::from_slice(&[]),
+        RocList<RocStr>
+    );
+}