This is article number 15 in a series of 21 articles on tools for evidence informed health policymaking. Monitoring is the term commonly used to describe the process of systematically collecting data that can inform policymakers, managers and other stakeholders as to whether a new policy or programme is progressing in accordance with their expectations. Data that are used for monitoring purposes are used as indicators to judge, for example, if objectives are being achieved, or if allocated funds are being spent appropriately. The term evaluation is sometimes used inter-changeably with monitoring. However, the term impact evaluation usually implies that there is a specific attempt to try to determine whether the observed changes in outcomes can be attributed to a particular policy or programme.