The Common International Classification of Ecosystem Services (CICES) developed from the work on environmental accounting undertaken by the European Environment Agency (EEA). It supports their contribution to the revision of the System of Environmental-Economic Accounting (SEEA) which is currently being led by the United Nations Statistical Division (UNSD). The idea of a common international classification is an important one, because it was recognised that if ecosystem accounting methods were to be developed and comparisons made, then some standardisation in the way we describe ecosystem services was needed. Standardisation was seen as especially important where the link to economic accounting has to be made. Since the original proposal interest in CICES has grown. It has now become clear that in addition to the need for standardization in the context of environmental accounting, work on mapping and valuing ecosystem services and ecosystems assessments more generally would benefit from more systematic approaches to naming and describing ecosystem services. The first fully operational version CICES (V4.3) was published in 2013. On the basis of the experience gained since then by the user community, its structure and scope has been reviewed, and as a result of an extensive period of consultation and peer review, CICES V5.1 is now available. The revision has ensured that new version is consistent with but extends CICES V4.3. The two versions are fully cross referenced and consistent with SEEA Principles. Broad equivalences between CICES classes and the categories of the MA, TEEB and IPBES classifications are also available.