diff --git a/javascript/ql/lib/change-notes/2024-11-20-ES2024-group-functions.md b/javascript/ql/lib/change-notes/2024-11-20-ES2024-group-functions.md
new file mode 100644
index 000000000000..8511727f8e77
--- /dev/null
+++ b/javascript/ql/lib/change-notes/2024-11-20-ES2024-group-functions.md
@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Added taint-steps for `Map.groupBy` and `Object.groupBy`.
diff --git a/javascript/ql/lib/semmle/javascript/Collections.qll b/javascript/ql/lib/semmle/javascript/Collections.qll
index a0e251554ff7..028c3abe4b3b 100644
--- a/javascript/ql/lib/semmle/javascript/Collections.qll
+++ b/javascript/ql/lib/semmle/javascript/Collections.qll
@@ -151,4 +151,32 @@ private module CollectionDataFlow {
       )
     }
   }
+
+  /**
+   * A step for a call to `groupBy` on an iterable object.
+   */
+  private class GroupByTaintStep extends TaintTracking::SharedTaintStep {
+    override predicate heapStep(DataFlow::Node pred, DataFlow::Node succ) {
+      exists(DataFlow::MethodCallNode call |
+        call = DataFlow::globalVarRef(["Map", "Object"]).getAMemberCall("groupBy") and
+        pred = call.getArgument(0) and
+        (succ = call.getCallback(1).getParameter(0) or succ = call)
+      )
+    }
+  }
+
+  /**
+   * A step for handling data flow and taint tracking for the groupBy method on iterable objects.
+   * Ensures propagation of taint and data flow through the groupBy operation.
+   */
+  private class GroupByDataFlowStep extends PreCallGraphStep {
+    override predicate storeStep(DataFlow::Node pred, DataFlow::SourceNode succ, string prop) {
+      exists(DataFlow::MethodCallNode call |
+        call = DataFlow::globalVarRef("Map").getAMemberCall("groupBy") and
+        pred = call.getArgument(0) and
+        succ = call and
+        prop = mapValueUnknownKey()
+      )
+    }
+  }
 }
diff --git a/javascript/ql/test/library-tests/TaintTracking/BasicTaintTracking.expected b/javascript/ql/test/library-tests/TaintTracking/BasicTaintTracking.expected
index 3d4fd0b67f86..b6d5ab1e435c 100644
--- a/javascript/ql/test/library-tests/TaintTracking/BasicTaintTracking.expected
+++ b/javascript/ql/test/library-tests/TaintTracking/BasicTaintTracking.expected
@@ -248,8 +248,19 @@ typeInferenceMismatch
 | tst.js:2:13:2:20 | source() | tst.js:66:10:66:16 | xSorted |
 | tst.js:2:13:2:20 | source() | tst.js:68:10:68:23 | x.toReversed() |
 | tst.js:2:13:2:20 | source() | tst.js:70:10:70:18 | xReversed |
-| tst.js:2:13:2:20 | source() | tst.js:72:10:72:17 | x.with() |
-| tst.js:2:13:2:20 | source() | tst.js:74:10:74:14 | xWith |
+| tst.js:2:13:2:20 | source() | tst.js:72:10:72:31 | Map.gro ... z => z) |
+| tst.js:2:13:2:20 | source() | tst.js:74:10:74:34 | Object. ... z => z) |
+| tst.js:2:13:2:20 | source() | tst.js:78:55:78:58 | item |
+| tst.js:2:13:2:20 | source() | tst.js:79:14:79:20 | grouped |
+| tst.js:2:13:2:20 | source() | tst.js:100:10:100:17 | x.with() |
+| tst.js:2:13:2:20 | source() | tst.js:102:10:102:14 | xWith |
+| tst.js:75:22:75:29 | source() | tst.js:75:10:75:52 | Map.gro ... (item)) |
+| tst.js:75:22:75:29 | source() | tst.js:75:47:75:50 | item |
+| tst.js:82:23:82:30 | source() | tst.js:83:58:83:61 | item |
+| tst.js:82:23:82:30 | source() | tst.js:84:14:84:20 | grouped |
+| tst.js:87:22:87:29 | source() | tst.js:90:14:90:25 | taintedValue |
+| tst.js:93:22:93:29 | source() | tst.js:96:14:96:25 | taintedValue |
+| tst.js:93:22:93:29 | source() | tst.js:97:14:97:26 | map.get(true) |
 | xml.js:5:18:5:25 | source() | xml.js:8:14:8:17 | text |
 | xml.js:12:17:12:24 | source() | xml.js:13:14:13:19 | result |
 | xml.js:23:18:23:25 | source() | xml.js:20:14:20:17 | attr |
diff --git a/javascript/ql/test/library-tests/TaintTracking/DataFlowTracking.expected b/javascript/ql/test/library-tests/TaintTracking/DataFlowTracking.expected
index 33a27661ecd1..3b89229b2d7f 100644
--- a/javascript/ql/test/library-tests/TaintTracking/DataFlowTracking.expected
+++ b/javascript/ql/test/library-tests/TaintTracking/DataFlowTracking.expected
@@ -112,3 +112,5 @@
 | thisAssignments.js:7:19:7:26 | source() | thisAssignments.js:8:10:8:20 | this.field2 |
 | tst.js:2:13:2:20 | source() | tst.js:4:10:4:10 | x |
 | tst.js:2:13:2:20 | source() | tst.js:54:14:54:19 | unsafe |
+| tst.js:93:22:93:29 | source() | tst.js:96:14:96:25 | taintedValue |
+| tst.js:93:22:93:29 | source() | tst.js:97:14:97:26 | map.get(true) |
diff --git a/javascript/ql/test/library-tests/TaintTracking/tst.js b/javascript/ql/test/library-tests/TaintTracking/tst.js
index 13b4ea48d8dd..8fbc5e525bd7 100644
--- a/javascript/ql/test/library-tests/TaintTracking/tst.js
+++ b/javascript/ql/test/library-tests/TaintTracking/tst.js
@@ -69,6 +69,34 @@ function test() {
     const xReversed = x.toReversed();
     sink(xReversed) // NOT OK
 
+    sink(Map.groupBy(x, z => z)); // NOT OK
+    sink(Custom.groupBy(x, z => z)); // OK
+    sink(Object.groupBy(x, z => z)); // NOT OK
+    sink(Map.groupBy(source(), (item) => sink(item))); // NOT OK
+
+    { 
+        const grouped = Map.groupBy(x, (item) => sink(item)); // NOT OK
+        sink(grouped); // NOT OK
+    }
+    {
+        const list = [source()];
+        const grouped = Map.groupBy(list, (item) => sink(item)); // NOT OK
+        sink(grouped); // NOT OK
+    }
+    {
+        const data = source();
+        const result = Object.groupBy(data, item => item);
+        const taintedValue = result[notDefined()];
+        sink(taintedValue); // NOT OK
+    }
+    {
+        const data = source();
+        const map = Map.groupBy(data, item => item);
+        const taintedValue = map.get(true); 
+        sink(taintedValue); // NOT OK
+        sink(map.get(true)); // NOT OK
+    }
+
     sink(x.with()) // NOT OK
     const xWith = x.with();
     sink(xWith) // NOT OK