This thesis explores the enabling role of bureaucracy in cross-expertise collaboration. Based on 13 months of ethnographic fieldwork in the engineering unit of an aeronautical company, and focusing on a myriad of different specialists involved in the company’s product development, I show that bureaucracy (i.e., understood as the rationalization of work) provides the infrastructure for the collaborative work of various experts. More specifically, through eight embedded cases, I examine how bureaucracy shapes cross-domain meetings, knowledge exchanges, and the work of intermediaries, making these dynamics more unambiguous, calculable, reliable, and precise. By reducing uncertainty, bureaucracy enables specialists to engage in focused and productive exchanges and interactions. I identify three conditions that underpin the positive impact of bureaucracy in this context and present four of its enabling roles in cross-expertise collaboration. Namely, these are: clarifying responsibilities, interconnections, and complex processes; promoting impartial relations and reducing tensions; ensuring participation in systemic matters; and streamlining integration. Overall, the thesis takes bureaucracy out of the shadows in our understanding of collaboration processes. It also contributes to studies on expertise coordination by highlighting that in highly-interdependent work situations formal organizational elements co-exist — and complement — emergent integration/coordination mechanisms. The thesis also contributes to the general organizational scholarship by putting forward a more appropriate understanding of bureaucracy in contemporary organizations which underscores its multifaceted nature. The work also has implications for the practitioner-oriented literature on collaboration, emphasizing the value of functional structures and formalization when most authors sing the praises of team-based arrangements and ‘organic’ structures.