Does familiarity with alliance partners promote breakthrough innovations? This study draws on the literature of interorganizational routines to examine the impact of repeated R&D collaborations within a firm's alliance portfolio on its breakthrough innovations. Specifically, we contend that the benefits and liabilities of interorganizational routines, arising from alliance partner repeatedness at a firm's alliance portfolio level, lead to an inverted U-shaped relationship between alliance partner repeatedness and breakthrough innovations. Further, we build on the recent theoretical development of interorganizational routines to propose that technological dynamism will make the inverted U-shaped relationship steeper. Analyses of approximatel...