A program's infrastructure is often cited as critical to public health success. The Component Model of Infrastructure (CMI) identifies evaluation as essential under the core component of engaged data. An evaluation plan is a written document that describes how to monitor and evaluate a program, as well as how to use evaluation results for program improvement and decision making. The evaluation plan clarifies how to describe what the program did, how it worked, and why outcomes matter. We use the Centers for Disease Control and Prevention's (CDC) "Framework for Program Evaluation in Public Health" as a guide for developing an evaluation plan. Just as using a roadmap facilitates progress on a long journey, a well-written evaluation plan can clarify the direction your evaluation takes and facilitate achievement of the evaluation's objectives.