diff --git a/ui.h b/ui.h
new file mode 100644
index 0000000..537e21a
--- /dev/null
+++ b/ui.h
@@ -0,0 +1,41 @@
+#pragma once
+
+#include "types.h"
+#include "util/vector.h"
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+typedef struct _App App;
+
+typedef enum {
+	ui_Running,
+	ui_Paused,
+	ui_TitleMenu,
+	ui_StateCount // Keep at last
+} ui_States;
+
+
+// Forward declarations
+typedef struct _ui_Button ui_Button;
+typedef struct _System_UI System_UI;
+
+// a Part of the UI.
+typedef struct {
+	void *user;                               // user data
+	void (*draw)(System_UI *sys, void *user); // called when the UI is to be drawn
+} ui_Part;
+
+// UI system with its own state machine.
+typedef struct _System_UI {
+	App           *super;
+	vector_Vector *parts[ui_StateCount];
+} System_UI;
+
+
+#ifdef __cplusplus
+}
+#endif