Universities across the globe have begun to invest in transdisciplinary research: a complex form of collaboration that places divergent disciplinary specialists and community members in participatory research aimed at addressing an applied research question. For a collaboration to succeed in this knowledge work, participants must engage in radical boundary crossing among disciplinary and community knowledge cultures wherein language is the substance of these boundaries and crossings. Effective collaboration, communication, and writing are essential to the success of transdisciplinary research, but composition research on collaborative writing has yet to address what collaboration looks like in transdisciplinary settings. This article offers a theoretical synthesis that brings transdisciplinary research theory into conversation with composition theory and pedagogy by providing an overview of the core principles of transdisciplinary research, offering an activity systems interpretation of transdisciplinary research, and outlining a framework for incorporating transdisciplinary collaboration into university composition programs.