Platforms enable and drive the creation of new products and services; they also shape and transform industries in fundamental ways. Consequently, platforms have become a core feature of many emerging business models. The success of a platform is inextricably linked to its network, or ecosystem, of enablers and complementors. Drawing on models and theories of complex systems, innovation, and network analysis, this study analyzes the evolving structure of interfirm relations in the mobile device platform ecosystem. This domain is of particular interest due to the emergence of promising new platforms and competition for platform leadership between open and closed business models. The visual approach presented in this study provides insights to the complexity of interfirm relations in the mobile device platform ecosystem, determines a platform’s competitive position, and identifies structural configurations that characterize various types of business strategies. Both theoretical and practical implications are discussed.