This dissertation is focused on the study of heterogeneous network performance. For decades, most strategy and organizational research has focused on understanding how networks influence a single “node,” typically an organization or individual. In contrast, I shift my perspective to view a whole network as the unit of analysis. This approach is designed to deepen scholarly understanding of strategic outcomes and collective performance that only exist at the higher level – the whole network level. The motivation for this dissertation is the realization many of society’s most complex problems and Grand Challenges require the concerted efforts of organizations towards shared goals, which may not always coincide with local (organization level) incentives. As such, I use the context of healthcare reform in the United States to examine how analyzing the complex patterns of interorganizational patient care may help us better understand the determinants of emergent outcomes at the whole network level. Specifically, the Affordable Care Act of 2010 led to the formation of hundreds of new interorganizational networks, called Accountable Care Organizations, within the Medicare system. Using patient treatment networks based on claims data, I examine two research questions. First, what are the relationships among various network level properties and collective performance? Second, how did the formation of Accountable Care Organizations alter existing patient care patterns and outcomes, if at all? In sum, this dissertation makes theoretical contributions to the study of organizational networks, particularly with regards to network level outcomes. Moreover, this research offers insights into how network studies may inform policy and practice in healthcare.