A unitary state is a state governed as a single power in which the central government is ultimately supreme and any administrative divisions (sub-national units) exercise only the powers that the central government chooses to delegate. The majority of states in the world have a unitary system of government. Of the 193 UN member states, 165 are governed as unitary states.
In a unitary state, sub-national units are created and abolished (an example being the 22 mainland regions of France being merged into 13), and their powers may be broadened and narrowed, by the central government. Although political power may be delegated through devolution to local governments by statute, the central government remains supreme; it may abrogate the acts of devolved governments or curtail their powers.
Unitary states are contrasted with federations, or federal states. In such states, the sub-national governments share powers with the central government as equal actors through a written constitution, to which the consent of both is required to make amendments. This means that the sub-national units have a right of existence and powers that cannot be unilaterally changed by the central government.
^Devolution within a unitary state, like federalism may be symmetrical, with all sub-national units having the same powers and status, or asymmetric, with sub-national units varying in their powers and status.