The Canadian theoretical psychologist, William (Bill) Rozeboom, published extensively in the disciplines of psychology and philosophy of science. Influenced in good part by his commitment to a logical empiricist philosophy of science, Rozeboom wrote articles of a technical nature in the belief that the precise, formal explication of methodological and substantive concepts held greater promise for the advancement of their understanding than relying on the vagaries of everyday language. This encyclopedia entry describes and evaluates a limited selection of Rozeboom’s many theoretical contributions, focusing primarily on those of direct relevance to psychology. The main topics featured are (1) the merits of the philosophy of logical empiricism; (2) the infirmities of the hypothetico-deductive method; (3) the limitations of null hypothesis tests of statical significance; (4) the importance of explanatory inference in science; (5) the structure of psychological theory; (6) the nature of behavior theory; and (7) the conceptual foundations of psychometric concepts. Two important recurring themes in Rozeboom’s work surface in this entry: a commitment to the philosophy of logical empiricism, with its focus on theory, and a strong emphasis on the importance of explanatory inference in science.