Evaluations are crucial in determining a program's impact and in identifying aspects of the program that should be modified or eliminated to better achieve program goals. Evaluations can also help determine whether the planned activities have been implemented and whether the program has reached its audience, changed attitudes or behaviors, increased knowledge, and addressed the targeted problem. Common evaluation techniques are interviews with stakeholders, analysis of existing data, onsite program reviews, reviews of program materials and reports, and surveys of key groups. The evaluation design and techniques should be determined in the course of the initial planning and design of the program. Because an evaluation essentially answers questions about the program, these questions should be formulated at the outset. They should be appropriate for the program and clearly linked to the program's goals and objectives. Further, the evaluation must determine the information needed to answer the evaluation questions and how and when this information is to be obtained. Data must be collected consistently and accurately, and the data should measure only what can be used; moreover, the evaluation should use only what has been measured. The paper concludes with an overview of the challenges and rewards of an evaluation.