Nonprofits are guided by internal efforts and external mandates to build capacity. However, scholars and grant makers are hampered by varied definitions of the concept, competing but untested models, and the lack of a reliable and valid measure. This research defines nonprofit capacity as the processes, practices, and people that the organization has at its disposal that enable it to produce, perform, or deploy resources to achieve its mission. An inductive-confirmatory two-study approach introduces and validates the Nonprofit Capacities Instrument, a 45-item measure of eight nonprofit capacities derived from existing instruments. The capacities are (1) financial management, (2) adaptive capacity, (3) strategic planning, (4) external communication, (5) board leadership, (6) operational capacity, (7) mission orientation, and (8) staff management. Intriguingly, this research demonstrates that nonprofit capacity is not a singular or second-order concept, but better described in its plural form, nonprofit capacities.CAPACITY-BUILDING INITIATIVES ARE common across nonprofit organizations, with numerous organizations and programs designed to improve capacity (e.g., Americorp CTC Vista, National Council of Nonprofi ts). In spite of this signifi cant investment, there is no unifying defi nition or model of nonprofi t capacity (Christensen and Gazley 2008 ). Moreover, both researchers and funders lack the ability to compare similar organizations ' capacity or the relative eff ectiveness of diff erent capacity-building initiatives.The purpose of this research is to introduce the Nonprofit Capacities Instrument, a selfreport measure of capacity that allows researchers, foundations, and practitioners to compare the capacities of nonprofit organizations using a standard metric. This research makes two contributions. First, we introduce a model of nonprofit capacity and demonstrate that it should be understood as interrelated nonprofit capacities , not as a second-order multidimensional construct (i.e., a single concept composed of multiple subdimensions claimed by existing conceptual models). Second and relatedly, this research answers Brown ' s ( 2012 ) call for a self-guided instrument that would allow for practitioners to assess their capacity without the need for external facilitation.