Governments and other organizations that design, implement, or manage in-service teacher professional development (TPD) programs navigate many choices and challenges to build monitoring and evaluation (M&E) systems that suit their program objectives and constraints. The primary objective of a TPD M&E system is to help guide the program toward its objectives of improved teaching practice, better quality student-teacher interactions, and, ultimately, improved student learning outcomes. An M&E system can help guide the TPD intervention toward these objectives by providing valuable data to feed into the design and implementation of the program. These data offer opportunities for course correction and could strengthen accountability relationships among stakeholders. This technical guidance note sets out how to navigate some of the challenges that governments and other organizations may face when designing and implementing an M&E system for an in-service TPD program. The specific design features of a TPD M&E system may vary depending on contextual factors. These factors include available resources, local technical capacity, political environment, fragile contexts, and the exact features of the TPD program--from "highly structured" to "low structured"; and school- and cluster-based versus other models. This note presents high-level guidance on key factors to consider when designing an effective M&E system for a TPD program.