There is a kind of power no one should have over anyone else, even if they don\u27t do anything with this power, or even if they only use this power for good. The republican tradition of political philosophy calls this kind of power domination. Here, I develop a theory of domination, and use this theory to advance our understanding of political legitimacy and justification. My account of domination refines recent neo-republican attempts to identify dominating social power with the capacity to interfere arbitrarily with the choices of others. I argue that this capacity is not sufficient for domination. Instead, domination requires that one agent possess impositional power over someone else: power enough to make their refusal to cooperate m...