This article describes the categories and typologies as an optic for looking at concept formation and measurement. It also provides an overview of the multiple contributions of typologies and presents numerous examples from diverse subfields of political science. It gives a framework for working with multidimensional typologies, outlining the building blocks of typologies, and illustrating how the cell types constitute categorical variables. In addition, the role of typologies in concept formation, the source of the concepts and terms in the cells of the typology, and the role of ideal types are explained. Finally, it explores the contribution of typologies to mapping empirical and theoretical change and to structuring comparison in empirical analysis. It suggests norms for the careful use of typologies. Among the guidelines for careful work with typologies, a significant priority to keep clearly in view is their contribution to wider goals of formulating and evaluating explanatory claims.