Quality improvement collaboratives have become a common strategy for improving health care. This paper uses social network analysis to study the relationships among organizations participating in a large scale public-private collaboration among major health plans to reduce racial and ethnic disparities in health care in the United States. Pre-existing ties, the collaborative process, participants' perceived contributions, and the overall organizational standing of participants were examined. Findings suggest that sponsors and support organizations, along with a few of the health plans, form the core of this network and act as the "glue" that holds the collaboration together. Most health plans (and one or two support organizations) are in the periphery. While health plans do not interact much with one another, their interactions with the core organizations provided a way of helping achieve health plans' disparities goals. The findings illustrate the role sponsors can play in encouraging organizations to voluntarily work together to achieve social ends while also highlighting the challenges.