Indiana University-Purdue University Indianapolis (IUPUI) / Nonprofit organizations that “speak for, act for, and look after the interests of their constituents when they interact with government are, by any definition of political science, interest groups.” Indiana’s recent implementation of the Healthy Indiana Plan 2.0 (HIP 2.0) under the Affordable Care Act (ACA) opened a window of opportunity to closely examine the role of nonprofits in shaping the implementation of health care policy. Existing literature on health and human service nonprofit organizations did not examine in depth the role and influence of nonprofits as interest groups in the implementation of public policy. This study examines a deeper research question that was not given adequate attention under existing studies with a special focus on the health care policy field: whose interest do nonprofit organizations advance when they attempt to influence the implementation of public policy? To answer this question, it is critical to understand why nonprofits engage in the public policy process (motivation and values), the policy actions that nonprofits make during the implementation of the policy (how?), and the method by which nonprofits address or mitigate conflicts and contradictions between organizational interest and constituents’ interest (whose interest do they advance?). The main contribution of this study is that it sheds light on the implementation of the largest extension of domestic social welfare policy since the “War on Poverty” using Robert Alford’s theory of interest groups to examine the role of nonprofit organizations during the implementation of HIP 2.0 in Indiana. Given the complexity of the policy process, this study utilizes a qualitative methods approach to complement existing quantitative findings. Finally, this study provides a deeper examination of the relationships between nonprofits as actors within a policy field, accounts for the complexity of the policy and political environment, analyzes whether or not dominant interest groups truly advance the interest of their constituents, and provides additional insights into how nonprofits mitigate and prioritize competing interests.