This paper develops relational pluralism as a collective construct whose dimensions are heterogeneity, multiplexity, and asymmetry. Relational pluralism is instantiated in the board of directors, whose network of relationships influence a new venture's ability to establish external links beyond the networks of the founding team. We argue that relational pluralism speeds the establishment of a diverse alliance portfolio, which, in turn, speeds the attainment of major revenue milestones in a new firm. We examine these ideas in a population of de novo semiconductor firms and find that diverse alliance portfolios emerge faster when a board includes members with heterogeneous, multiplex relationships, as well as central network positions. However, the asymmetric influence of outside board members can have both positive and negative effects: the alliance formation process is aided by outsiders in central network positions, but impeded when central investors dominate the board. We discuss implications for our understanding of relational pluralism as a collective construct.