Nonprofit infrastructure organizations provide multiple functions to the nonprofit sector: strengthening individual and organizational capacities, mobilizing material resources, providing information and intellectual resources, building alliances for mutual support, bridging the research and practice divide, and connecting nonprofits to the other sectors. Although researchers have described a variety of organizations that support nonprofit activity, they have done little to distinguish them or to explain their primary purposes. In this article, we develop a typology to classify these nonprofit infrastructure organizations, which offers new insight into their various objectives and functions. Based on a review of the relevant literature and interviews with stakeholders, we then construct a necessary framework for the assessment of the infrastructure organizations we have identified. The result is a better understanding of not only the types of nonprofit infrastructure organizations but also the appropriate dimensions for their assessment.