Partial organization is a neat theoretical solution: it broadens the scope outside the formal organization and distinguishes between the organized and the non-decided. The purpose of this paper is to make a first, conceptual step towards exploring the drivers of partial organization and its expansion. We put partial organization in dialogue with other organizational theories and outline three different theoretical ways to explain why partial organization expands. First, the elaboration of organizational actorhood results in expanded partial organization. Second, new forms of organization, which deviate from the standard model of centralized organization, drive partial organization. And third, decided orders outside organizations perpetually expand, because they are based on decisions. Partial organization consequently expands for different reasons, but attention is focused on organizational expansion that satisfies Western principles, such as liberalisms and democracy. The theory of partial organization, however, would give us the tools to likewise analyze equally coercive sanctioning or power-laden hierarchies and to fully grasp organizational expansion. Mobilizing the lens of partial organization across Western contexts could bring the benefit of discovering cultural features and differences of organization, which in turn will increase the explanatory power of partial organization.