This document is the Copernicus Marine Environment Monitoring Service for In Situ observations System Requirements Document (CMES-INS-SRD). It specifies the capabilities of the CMEMS-INS system as a response to the CMEMS-INS system requirements. The Copernicus In Situ Thematic Assembly Centre (In Situ TAC) provides a research and operational framework to develop and deliver In Situ observations and derived products based on such observations, to address progressively global but also regional needs either for monitoring, modelling or downstream service development.