Scholars and practitioners agree that international nongovernmental organizations (INGOs) have become important actors in international relations and policymaking. But an understanding of INGOs' impact requires a step back, analyzing how and why they behave as they do. We develop a framework that sorts and links relevant factors into three interlocking layers: (1) internal traits of an INGO, (2) interactions between an INGO and other actors, and (3) the overall institutional environment that defines the boundaries of INGO action. To demonstrate the merits of the framework, we review and analyze Internal Affairs by Wendy Wong, The Opening Up of International Organizations by Jonas Tallberg et al., and Borders among Activists by Sarah Stroup. Locating each book within its intended scholarly context, we evaluate contributions to individual layers in our framework. We also examine ties among the books, examining how each work implicitly treats other layers. By uniting internal, interactive, and institutional factors into a holistic framework, we reveal links within existing work on INGOs and illuminate promising avenues for future work about these important actors.