Why are certain organization design arrangements enacted in a project-based organization? Building on extant literature, this article addresses this fundamental question by explicating three distinct explanations of the raison d'etre of salient organization design arrangements: Functional, Legitimacy, and Agency. Conceiving these explanations as coexisting, interacting logics of organizing, the article argues to draw upon the powerful concept of logic multiplicity to pave the way for integrating diverse theoretical perspectives. Thus, the article contributes to the organization design stream of research in project studies by developing a typology of organization design logics and proposing a way forward for pursuing pluralistic theorizing.