Gauging impact is one of the most consistently problematic and elusive issues facing the social sector today. Governmental bodies, foundations, individual donors, and other funders increasingly demand information on the use of program funds, and the program's overall impact, but how can we determine whether a program is working?This book provides processes and tools that agencies of all kinds can apply to obtain valid, reliable, and credible data to address questions about the performance of public and nonprofit programs. It allows for the systematic assessment of program results, and to the extent feasible, systematic assessment of the extent to which the program caused those results.