In light of rapidly changing customer demands, technological uncertainty, as well as more complex and geographically dispersed value chains, firms in many industries are increasingly questioning their once prevailing strategy of operating within their organizational boundaries. As a result, most firms today are simultaneously engaged in various collaborative arrangements with customers, suppliers, competitors, and research institutes located across the globe in order to get access to complementary resources, capabilities, and new markets (Goerzen, 2005; Lavie, 2007; Liu, Ghauri, & Sinkovics, 2010; Wassmer, 2010). To capture the realities of firms’ multifaceted and complex collaboration activities, research has gradually shifted from the study of dyadic alliances to the examination of alliance portfolios (Goerzen & Beamish, 2005; Jiang, Tao, & Santoro, 2010; Srivastava & Gnyawali, 2011). The analytical value of taking the alliance portfolio, i.e. ‘‘a firm’s collection of immediate alliance partners’’ (Lavie & Miller, 2008, p. 623) as the unit of analysis lies in accounting for interdependencies between a firm’s different alliances (Goerzen, 2005; Hoffmann,2007; Wassmer, 2010) 1 . Managing an alliance portfolio is not only associated with different tasks, decisions, and challenges than managing an individual alliance, but also has different performance implications arising from synergistic effects (Wang & Rajagopalan, 2015; Wuyts & Dutta, 2014). A portfolio perspective is particularly fruitful for studies seeking to explain aggregate firmlevel outcomes such as financial or innovative performance, which are a function of the sum of a firm’s alliances rather than isolated alliances.

This study seeks to answer the question of how and under what conditions alliance portfolio partner diversity influences firms’ innovative performance as reflected in the revenue share from new-to-market products and services. Previous research has provided valuable insights into the emergence, management, and effectiveness of alliance portfolios of varying size, partner characteristics, as well as structural attributes (see Wassmer, 2010 for a review). Yet, at the same time, empirical evidence on the performance effects of alliance portfolios is mixed andinconclusive. In particular, studies examining how different forms of alliance portfolio diversity (e.g., industry and technological partner diversity) affect firms’ innovative performance have reported either positive (De Leeuw, Lokshin, & Duysters, 2014; Srivastava & Gnyawali, 2011), U-shaped (Wuyts & Dutta, 2014), or inverted U-shaped (De Leeuw et al., 2014; Vasudeva & Anand, 2011) relationships. On the one hand, these inconsistent findings are reflective of the opposing arguments on the benefits (e.g., access to new perspectives and complementary resources) and costs (e.g., complexity, coordination issues, and value appropriation concerns) of maintaining large and diverse alliance portfolios (Baum, Calabrese, & Silverman, 2000; Hoffmann, 2007; Lee, Kirkpatrick-Husk, & Madhavan, 2014). On the other hand, a growing number of studies specifically suggest that it is necessary to adopt a contingency perspective on alliance portfolio performance rather than looking for generalizable main effects. Accordingly, the benefits of alliance portfolios have been found to be contingent not only on partner characteristics, but also on the strategies, structural characteristics, and technological resources of the focal firm (Lavie & Miller, 2008; Wuyts & Dutta, 2014; Yamakawa, Yang, & Lin, 2011). However, research on the moderating role of focal firm characteristics is still in its infancy (e.g., Srivastava & Gnyawali, 2011).

In order to further resolve the inconsistent relationship between alliance portfolio diversity and performance, we draw on the resource-based view (RBV) of the firm (Barney, 1991; Peteraf, 1993). By shedding light on the role of collaboration partners’ resources in value creation, the RBV provides a useful theoretical lens for understanding the innovation effects of alliance portfolios. We focus our analysis on multinational companies to account for the unique resource characteristics of these firms and explore potential differences between MNCs and domestic firms in their ability to capture the benefits of alliance portfolios. Based on the RBV and in line with the international business literature that argues that MNCs possess superior financial, structural, managerial, and technological resources and have a competitive advantage compared to their local counterparts (Buckley & Casson, 1976; Dunning, 1988), we expect such differences to exist. Initial evidence shows that the structural attributes of an MNC (i.e., subsidiary network) indeed play a key role in realizing value from alliance portfolios (Zaheer & Hernandez, 2011).