diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.cpp
index af2815abf3..57ac3447f7 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.cpp
@@ -40,6 +40,7 @@ void PlainYearMonthPrototype::initialize(GlobalObject& global_object)
     define_native_accessor(vm.names.eraYear, era_year_getter, {}, Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
+    define_native_function(vm.names.with, with, 1, attr);
     define_native_function(vm.names.equals, equals, 1, attr);
     define_native_function(vm.names.toString, to_string, 0, attr);
     define_native_function(vm.names.toLocaleString, to_locale_string, 0, attr);
@@ -186,6 +187,49 @@ JS_DEFINE_NATIVE_FUNCTION(PlainYearMonthPrototype::era_year_getter)
     return TRY(calendar_era_year(global_object, calendar, *plain_year_month));
 }
 
+// 9.3.11 Temporal.PlainYearMonth.prototype.with ( temporalYearMonthLike [ , options ] ), https://tc39.es/proposal-temporal/#sec-temporal.plainyearmonth.prototype.with
+JS_DEFINE_NATIVE_FUNCTION(PlainYearMonthPrototype::with)
+{
+    auto temporal_year_month_like = vm.argument(0);
+
+    // 1. Let yearMonth be the this value.
+    // 2. Perform ? RequireInternalSlot(yearMonth, [[InitializedTemporalYearMonth]]).
+    auto* year_month = TRY(typed_this_object(global_object));
+
+    // 3. If Type(temporalYearMonthLike) is not Object, then
+    if (!temporal_year_month_like.is_object()) {
+        // a. Throw a TypeError exception.
+        return vm.throw_completion<TypeError>(global_object, ErrorType::NotAnObject, temporal_year_month_like.to_string_without_side_effects());
+    }
+
+    // 4. Perform ? RejectObjectWithCalendarOrTimeZone(temporalYearMonthLike).
+    TRY(reject_object_with_calendar_or_time_zone(global_object, temporal_year_month_like.as_object()));
+
+    // 5. Let calendar be yearMonth.[[Calendar]].
+    auto& calendar = year_month->calendar();
+
+    // 6. Let fieldNames be ? CalendarFields(calendar, « "month", "monthCode", "year" »).
+    auto field_names = TRY(calendar_fields(global_object, calendar, { "month"sv, "monthCode"sv, "year"sv }));
+
+    // 7. Let partialYearMonth be ? PreparePartialTemporalFields(temporalYearMonthLike, fieldNames).
+    auto* partial_year_month = TRY(prepare_partial_temporal_fields(global_object, temporal_year_month_like.as_object(), field_names));
+
+    // 8. Set options to ? GetOptionsObject(options).
+    auto* options = TRY(get_options_object(global_object, vm.argument(1)));
+
+    // 9. Let fields be ? PrepareTemporalFields(yearMonth, fieldNames, «»).
+    auto* fields = TRY(prepare_temporal_fields(global_object, *year_month, field_names, {}));
+
+    // 10. Set fields to ? CalendarMergeFields(calendar, fields, partialYearMonth).
+    fields = TRY(calendar_merge_fields(global_object, calendar, *fields, *partial_year_month));
+
+    // 11. Set fields to ? PrepareTemporalFields(fields, fieldNames, «»).
+    fields = TRY(prepare_temporal_fields(global_object, *fields, field_names, {}));
+
+    // 12. Return ? YearMonthFromFields(calendar, fields, options).
+    return TRY(year_month_from_fields(global_object, calendar, *fields, options));
+}
+
 // 9.3.16 Temporal.PlainYearMonth.prototype.equals ( other ), https://tc39.es/proposal-temporal/#sec-temporal.plainyearmonth.prototype.equals
 JS_DEFINE_NATIVE_FUNCTION(PlainYearMonthPrototype::equals)
 {
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.h b/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.h
index 4dc0ed0135..143a8a8dc3 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.h
@@ -30,6 +30,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(in_leap_year_getter);
     JS_DECLARE_NATIVE_FUNCTION(era_getter);
     JS_DECLARE_NATIVE_FUNCTION(era_year_getter);
+    JS_DECLARE_NATIVE_FUNCTION(with);
     JS_DECLARE_NATIVE_FUNCTION(equals);
     JS_DECLARE_NATIVE_FUNCTION(to_string);
     JS_DECLARE_NATIVE_FUNCTION(to_locale_string);
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainYearMonth/PlainYearMonth.prototype.with.js b/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainYearMonth/PlainYearMonth.prototype.with.js
new file mode 100644
index 0000000000..2953a2baa7
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainYearMonth/PlainYearMonth.prototype.with.js
@@ -0,0 +1,57 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.PlainYearMonth.prototype.with).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        const plainYearMonth = new Temporal.PlainYearMonth(1970, 1);
+        const values = [
+            [{ year: 2021 }, new Temporal.PlainYearMonth(2021, 1)],
+            [{ year: 2021, month: 7 }, new Temporal.PlainYearMonth(2021, 7)],
+            [{ year: 2021, monthCode: "M07" }, new Temporal.PlainYearMonth(2021, 7)],
+        ];
+        for (const [arg, expected] of values) {
+            expect(plainYearMonth.with(arg).equals(expected)).toBeTrue();
+        }
+
+        // Supplying the same values doesn't change the year/month, but still creates a new object
+        const plainYearMonthLike = { year: plainYearMonth.year, month: plainYearMonth.month };
+        expect(plainYearMonth.with(plainYearMonthLike)).not.toBe(plainYearMonth);
+        expect(plainYearMonth.with(plainYearMonthLike).equals(plainYearMonth)).toBeTrue();
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.PlainYearMonth object", () => {
+        expect(() => {
+            Temporal.PlainYearMonth.prototype.with.call("foo");
+        }).toThrowWithMessage(TypeError, "Not an object of type Temporal.PlainYearMonth");
+    });
+
+    test("argument must be an object", () => {
+        expect(() => {
+            new Temporal.PlainYearMonth(1970, 1).with("foo");
+        }).toThrowWithMessage(TypeError, "foo is not an object");
+        expect(() => {
+            new Temporal.PlainYearMonth(1970, 1).with(42);
+        }).toThrowWithMessage(TypeError, "42 is not an object");
+    });
+
+    test("argument must have one of 'month', 'monthCode', 'year'", () => {
+        expect(() => {
+            new Temporal.PlainYearMonth(1970, 1).with({});
+        }).toThrowWithMessage(
+            TypeError,
+            "Object must have at least one of the following properties: month, monthCode, year"
+        );
+    });
+
+    test("argument must not have 'calendar' or 'timeZone'", () => {
+        expect(() => {
+            new Temporal.PlainYearMonth(1970, 1).with({ calendar: {} });
+        }).toThrowWithMessage(TypeError, "Object must not have a defined calendar property");
+        expect(() => {
+            new Temporal.PlainYearMonth(1970, 1).with({ timeZone: {} });
+        }).toThrowWithMessage(TypeError, "Object must not have a defined timeZone property");
+    });
+});