This paper argues that historicism can provide substantive philosophical grounds for critical theory and various modes of critique. Unlike the developmental historicism that dominated the nineteenth century, we start from a radical historicism tied to nominalism, contingency, and contestability. This radical historicism is compatible with a commitment to truth claims, including the truth of historicism and the truth of particular genealogies and other accounts of the world. Genealogy can be viewed as radical historicism in its critical guise, denaturalizing the ideas it targets. In addition, however, radical historicism provides possible grounds for both historical ontology and a revised version of ideology critique. Ideology is conceived here in relation to failures in consciousness itself rather than the alleged conflicts of a material base.