This document provides several definitions and descriptions of evaluation. Evaluation is defined as the systematic acquisition and assessment of information to provide useful feedback, the examination of the worth or significance of an object, and the structured interpretation and giving of meaning to actual or predicted impacts. Evaluation can be formative, taking place during development to improve effectiveness, or summative, drawing lessons after completion. Evaluation involves applying scientific methods to assess design, implementation, outcomes, and value of programs in a rigorous and resource-intensive process. The key difference between evaluation and assessment is that evaluation uses assessment data to support decisions around maintaining, changing, or discarding practices.