In the enterprise software industry, large providers (hubs) are fostering partner networks with smaller companies (spokes) that complement their platforms. This study takes the perspective of these spokes and seeks to understand their motivation to partner. It is the first to simultaneously examine two theoretical perspectives that help explain partnership formation. The input-oriented perspective holds that organizations enter inter-firm arrangements in order to access external resources and capabilities. The output-oriented perspective posits that the complementarity of the partners ’ products influences the benefits obtained from a partnership. In order to examine the relevancy and possible interaction of these two perspectives, a multiple-case study is conducted. Qualitative data from 17 spoke organizations is gathered and thoroughly analyzed. The study confirms that the hub's reputation and its capability to provide integrated systems are generally important reasons for partnering. However, the extent to which the hub’s innovativeness and its commercial capital motivate spokes to partner varies substantially. The key finding of this study is that these variations can be explained by differences in the level of product complementarity. This leads to the