Historical ontology is a term associated with the philosopher of science Ian Hacking and gained currency among theoretical psychologists after he published a book with that title in 2002. Hacking advocated for historical ontology as an alternative framework for understanding the nature of those objects studied by the human sciences that steers between the poles of realism and relativism as introduced by theories of social construction. Psychology’s interactive kinds are simultaneously contingent and cultural while made real through the disparate practices of scientific investigation and the adoption of scientific categories among lay populations. The term’s debt to the genealogical work of Michel Foucault is discussed. Historical ontology is illustrated using Hacking’s philosophical history of multiple personality disorder as well as other examples from the history of psychology. The term is situated in the context of other historicizing approaches in theoretical psychology and psychologist’s concerns about the permissiveness of the concepts they introduce.