diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
index 215ee1db5f..7f16ead01b 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
@@ -5,6 +5,7 @@
  */
 
 #include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/Temporal/Calendar.h>
 #include <LibJS/Runtime/Temporal/CalendarPrototype.h>
 
 namespace JS::Temporal {
@@ -23,6 +24,35 @@ void CalendarPrototype::initialize(GlobalObject& global_object)
 
     // 12.4.2 Temporal.Calendar.prototype[ @@toStringTag ], https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype-@@tostringtag
     define_direct_property(*vm.well_known_symbol_to_string_tag(), js_string(vm.heap(), "Temporal.Calendar"), Attribute::Configurable);
+
+    u8 attr = Attribute::Writable | Attribute::Configurable;
+    define_native_function(vm.names.toString, to_string, 0, attr);
+}
+
+static Calendar* typed_this(GlobalObject& global_object)
+{
+    auto& vm = global_object.vm();
+    auto* this_object = vm.this_value(global_object).to_object(global_object);
+    if (!this_object)
+        return {};
+    if (!is<Calendar>(this_object)) {
+        vm.throw_exception<TypeError>(global_object, ErrorType::NotA, "Temporal.Calendar");
+        return {};
+    }
+    return static_cast<Calendar*>(this_object);
+}
+
+// 12.4.23 Temporal.Calendar.prototype.toString ( ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.tostring
+JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::to_string)
+{
+    // 1. Let calendar be the this value.
+    // 2. Perform ? RequireInternalSlot(calendar, [[InitializedTemporalCalendar]]).
+    auto* calendar = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Return calendar.[[Identifier]].
+    return js_string(vm, calendar->identifier());
 }
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h
index 4f17d1b68f..aa48b08ada 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h
@@ -17,6 +17,9 @@ public:
     explicit CalendarPrototype(GlobalObject&);
     virtual void initialize(GlobalObject&) override;
     virtual ~CalendarPrototype() override = default;
+
+private:
+    JS_DECLARE_NATIVE_FUNCTION(to_string);
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.toString.js b/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.toString.js
new file mode 100644
index 0000000000..cac3052267
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.toString.js
@@ -0,0 +1,18 @@
+describe("correct behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.Calendar.prototype.toString).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        expect(calendar.toString()).toBe("iso8601");
+    });
+});
+
+test("errors", () => {
+    test("this value must be a Temporal.Calendar object", () => {
+        expect(() => {
+            Temporal.Calendar.prototype.toString.call("foo");
+        }).toThrowWithMessage(TypeError, "Not a Temporal.Calendar");
+    });
+});