This publication clarifies the conceptual understanding of a circular economy from both the policy and the monitoring perspectives. The starting point is a short "headline definition" which highlights the interrelated features of all circular economy definitions: maintaining the value of materials in the economy for as long as possible whilst ensuring a positive outcome to society, and preserving natural capital (natural resources, environmental quality) and human health. The conceptual framework has four main components (material life cycle and value chain, interactions with the environment, socio-economic opportunities, and responses and actions). It is complemented with an initial set of indicators for monitoring progress towards a circular economy and a monitoring framework which discusses important measurement considerations, in particular the use of the System of Environmental Economic Accounting (SEEA) for measuring circular economy. The document also includes examples of measurement frameworks used by countries and other regional and national case examples on measuring the circular economy.