Extant scholarship in project studies is calling for fertilizing across disciplines to pave the way to stronger theorizing. This essay responds to this call by spurring a debate on how to theorize temporary organizing in new and creative ways — both broadly and with a particular focus on projects, arguably the most prevalent form of such organizing. We propose addressing projects and other forms of temporary organization as processual, practice-based phenomena that provide ample opportunities to foster cross-fertilization, in particular between the related disciplines of organization and project studies. To this end, we argue that theoretical advancements in a discipline can occur on a spectrum—ranging from leveraging reference theories from related fields (a top-down approach) to developing home-grown theories grounded in empirical research (a bottom-up approach). This spectrum serves as the foundation for this essay, as we develop this processual, practice-based perspective to project studies by illustrating how (1) reference theories from organization studies such as practice-driven institutionalism generate new insights on temporary organizing and (2) home-grown theories of temporary organizing generated by studying projects and other forms of temporary organization may have theoretical and practical implications beyond project studies.