Monitoring and evaluation are essential to gather information from past and current activities that aim to have a positive impact on sustainable development. Monitoring’s purpose is to track a development intervention’s progress, comparing what is delivered with what is planned. Evaluation has evolved from being a self-assessment exercise for development institutions to becoming a tool of impartial scrutiny of operations, reporting usually directly to governing bodies. The Sustainable Development Goals (SDGs) agreed by 193 countries in September 2015, which frame the international development agenda till 2030, benefit from a quarter of a century of evaluating efforts to achieve their predecessors, the Millennium Development Goals. The inherent complexity of the SDGs – and the lack of data for some indicators – implies that evaluators will have to come up with new sources and methods. The chapter also presents an overview of the key concepts discussed in this book.