This paper explores the contribution of the institutional perspective in understanding firm innovation returns from international alliances. It argues that formal and informal national institutions are of different nature, and give rise to explicit and tacit differences respectively between alliance partners. Partners exhibit different attitudes and abilities to negotiate and address such differences in leveraging the innovation potential of international alliances. As a result, we expect such differences to have distinct effects on partners' innovation performance: a) the effect of informal institutional differences is approximating sigmoid (S-shaped), with innovation performance slightly increasing first, then improving further and finall...