The Housing Partnership Network (HPN) is a peer network composed of 87 nonprofit organizations involved in affordable housing as developers, lenders, managers, and providers of services to their residents. The members most commonly produce rental housing for low-income people, operating at large scale and on a regional rather than neighborhood level, and aiming for a high degree of financial self-sufficiency. In aggregate, they form a significant portion of the nonprofit industry in their fields of work. This study reports for the first time on their substantial productivity, the ways they do business to achieve their results, and the policy issues facing them as they grow.