The supply chain literature has highlighted the role of internal integration (i.e., crossfunctional integration) and external integration (i.e., cross-firm integration) in coordinating operations, facilitating exchanges, and ultimately improving supply chain performance. Few studies however have considered both internal and external integration and even fewer have attempted to study the internal-external integration linkage. This research attempts to extend prior work by 1) studying purchasing and engineering integration and its role on integrating suppliers into new product development ventures and, 2) positing a specific mechanism linking internal and external integration: the development of social integration between purchasing and engineering.