How should evaluation be defined? What is its purpose? What are the key issues involved? Françoise Jabot, head of evaluation training at the National School of Public Health (ENSP), outlines here some essential features of the process: a collective and negotiated effort, the consideration of multiple perspectives, a rigorous methodology... Evaluation helps decision-makers “improve public management” and practitioners “improve their work.” The evaluator supports the evaluation process by reconstructing the rationale for action, clarifying objectives, and assisting in the selection or development of tools for data collection and analysis.