diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp
index 5880d900af..449f4f0f13 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
+ * Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -41,6 +42,7 @@ void PlainDatePrototype::initialize(GlobalObject& global_object)
     define_native_accessor(vm.names.inLeapYear, in_leap_year_getter, {}, Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
+    define_native_function(vm.names.getISOFields, get_iso_fields, 0, attr);
     define_native_function(vm.names.withCalendar, with_calendar, 1, attr);
     define_native_function(vm.names.equals, equals, 1, attr);
     define_native_function(vm.names.valueOf, value_of, 0, attr);
@@ -264,6 +266,34 @@ JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::in_leap_year_getter)
     return Value(calendar_in_leap_year(global_object, calendar, *temporal_date));
 }
 
+// 3.3.18 Temporal.PlainDate.prototype.getISOFields ( ), https://tc39.es/proposal-temporal/#sec-temporal.plaindate.prototype.getisofields
+JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::get_iso_fields)
+{
+    // 1. Let temporalDate be the this value.
+    // 2. Perform ? RequireInternalSlot(temporalDate, [[InitializedTemporalDate]]).
+    auto* temporal_date = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Let fields be ! OrdinaryObjectCreate(%Object.prototype%).
+    auto* fields = Object::create(global_object, global_object.object_prototype());
+
+    // 4. Perform ! CreateDataPropertyOrThrow(fields, "calendar", temporalDate.[[Calendar]]).
+    fields->create_data_property_or_throw(vm.names.calendar, Value(&temporal_date->calendar()));
+
+    // 5. Perform ! CreateDataPropertyOrThrow(fields, "isoDay", 𝔽(temporalDate.[[ISODay]])).
+    fields->create_data_property_or_throw(vm.names.isoDay, Value(temporal_date->iso_day()));
+
+    // 6. Perform ! CreateDataPropertyOrThrow(fields, "isoMonth", 𝔽(temporalDate.[[ISOMonth]])).
+    fields->create_data_property_or_throw(vm.names.isoMonth, Value(temporal_date->iso_month()));
+
+    // 7. Perform ! CreateDataPropertyOrThrow(fields, "isoYear", 𝔽(temporalDate.[[ISOYear]])).
+    fields->create_data_property_or_throw(vm.names.isoYear, Value(temporal_date->iso_year()));
+
+    // 8. Return fields.
+    return fields;
+}
+
 // 3.3.22 Temporal.PlainDate.prototype.withCalendar ( calendar ), https://tc39.es/proposal-temporal/#sec-temporal.plaindate.prototype.withcalendar
 JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::with_calendar)
 {
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.h b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.h
index 3691340905..73f2f97b93 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.h
@@ -33,6 +33,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(months_in_year_getter);
     JS_DECLARE_NATIVE_FUNCTION(in_leap_year_getter);
 
+    JS_DECLARE_NATIVE_FUNCTION(get_iso_fields);
     JS_DECLARE_NATIVE_FUNCTION(with_calendar);
     JS_DECLARE_NATIVE_FUNCTION(equals);
     JS_DECLARE_NATIVE_FUNCTION(value_of);
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDate/PlainDate.prototype.getISOFields.js b/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDate/PlainDate.prototype.getISOFields.js
new file mode 100644
index 0000000000..eaef972318
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDate/PlainDate.prototype.getISOFields.js
@@ -0,0 +1,19 @@
+describe("normal behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.PlainDate.prototype.getISOFields).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        const plainDate = new Temporal.PlainDate(2021, 7, 29, calendar);
+        const fields = plainDate.getISOFields();
+        expect(fields).toEqual({ calendar, isoDay: 29, isoMonth: 7, isoYear: 2021 });
+        // Test field order
+        expect(Object.getOwnPropertyNames(fields)).toEqual([
+            "calendar",
+            "isoDay",
+            "isoMonth",
+            "isoYear",
+        ]);
+    });
+});