The authors review the unique characteristics of nonprofit organizations and explain how nonprofit organizations play a prominent role in providing today's public services. The authors describe how the field of professional evaluation developed in response to government performance-based management initiatives, noting that recent efforts at the federal level--Government Performance and Results Act (GPRA) and the Program Assessment Rating Tool (PART) in particular--have "revived" program evaluation and brought outcomes measurement into the forefront of public and nonprofit management. The chapter concludes with a reflection on the last 30 years, noting key important developments, milestones, and trends in the field, including calls for more effective philanthropy, an increase in accessible evaluation training manuals and tools, and organized efforts to build the evaluation capacity of nonprofit organizations. (Contains 1 figure and 3 notes.)