Relevance, coherence, effectiveness, efficiency, impact, and sustainability are widely used evaluation criteria, particularly in international development co-operation. They help to determine the merit or worth of various interventions, such as strategies, policies, programmes or projects. This guidance aims to help evaluators and others to better understand those criteria, and improve their use. It starts by describing what they are, and how they are meant to be used. Then the definitions and concepts underpinning each criterion are explained. Finally, examples provide the reader with concrete ideas for using them. The criteria were originally laid out in the early 2000s by the Network on Development Evaluation (EvalNet) of the OECD Development Assistance Committee (DAC). Although they have been widely used in evaluation, and beyond, this document is the first to comprehensively explore the concepts in detail, explain their intended use and offer practical guidance. It captures current thinking and best practice in evaluation, drawing on the inputs of internationally renowned evaluation experts from EvalNet and beyond.