Abstract: Evaluation is the systematic investigation of the effects that your program has on the lives of people touched by your program. The process of designing an evaluation system benefits your program by clarifying your goals and identifying indicators of progress towards your goals. The results of evaluation provide program staff with important evidence that can shape a reflective process of iteration and improvement. The products of evaluation are also vital for demonstrating to philanthropists and grant-makers the value of their charitable investments. For many non-profit programs, evaluation is foreign and scary. We plunge into public service out of a passion for serving people, not because we want to gin up data for analysis. For those whose work depends upon the charity of others, evaluations run the risk of revealing weaknesses and limitations. Many people can be intimidated by the quantitative aspects of evaluation or feel that numerical summaries of work can obscure the transformative impact of programs on individual lives. But the best non-profit agencies are learning organizations, committed to a constant cycle of experiment, inquiry, reflection, and refinement. By studying our programs, testing our assumptions, and gathering evidence of our impact and shortcomings, we have the opportunity to do our work even better. We can use evaluation to engage a growing audience of philanthropists and grant-makers who want to invest in programs committed to gathering evidence of their effectiveness.