This document discusses the importance of using monitoring and evaluation (M&E) data to inform policy formulation, program planning, and improvement. It provides examples of how M&E data has been used in Nigeria to guide resource allocation and strengthen sub-national M&E systems. Barriers to data use include technical, organizational, individual, and political constraints. Ensuring data is effectively used requires understanding how it is produced and used, identifying and addressing barriers, and strengthening decision-making processes.