The evaluation planning process consists of a multitude of decisions. For outcome evaluations, these decisions typically include the identification of the major questions to be addressed, the specification of high-priority outcomes, the translation of those outcomes into measurement strategies and instruments, the determination of counterfactual comparisons, the identification of timelines, and the planning of strategies for examining and analyzing data, among others. These decisions will ultimately influence the accuracy of evaluation inferences and conclusions. Validity refers to the strength of those evaluative judgments and the level of confidence that can be placed in them. This book will help readers to understand these validity concepts and apply them in the decision-making processes of evaluation planning. Careful attention to these principles will result in stronger evaluations and a stronger evidence base that can be utilized in making program-related decisions.