Ideal theories of justice have been accused by contemporary non-ideal and realist theorists of an ideological character. In this paper, I examine how such a charge can be substantiated and argue that a successful critique of ideal theory as ideology must both identify a general property of ideal theories that accounts for a limitation of their critical powers, and must allow for the existence of an alternative form of critique that is sufficiently critical. I then consider the ideology critiques of Charles Mills and Raymond Geuss and conclude that they cannot meet these conditions. An more successful model can be found in the tradition of critical theory. I extract from this tradition a formal model of ideology which focuses on the reflective potentials of conceptual forms and a strategy of immanent critique that avoids the pitfalls of ideal theory but retains the critical power of its Utopian dimension.