Activity and occupation are two core concepts of occupational therapy that are in need of differentiation. Occupation is defined here as a person's personally constructed, one-time experience within a unique context. Activity is defined as a more general, culturally shared idea about a category of action. The ways in which subjectivity and context are handled within the concepts of occupation and activity are keys to disentangling them. The proposed untangling of the two concepts into distinct definitions is congruent with their historical origins as well as with current definitional trends. Once occupation and activity are recognized as two separate and equally valuable concepts, they offer a rich set of theoretical relations for exploration. The clarity that will result from differentiating occupation and activity will enhance disciplinary discourse and research as well as enhance the intervention efficacy, moral surety, and political strength of the profession.