The member states of the African Union are the 55 sovereign states that have ratified or acceded to the Constitutive Act of the African Union to become member states to the African Union (AU). The AU was the successor to the Organisation of African Unity (OAU), and AU membership was open to all OAU member states. The African Union is composed of fifty-two republics and three monarchies. The total population of the AU is 1,068,444,000 (2013).