This document specifies the NetCDF file format of Copernicus Marine In Situ used to distribute ocean in situ data and metadata. It documents the standards used herein; this includes naming conventions as well as metadata content. It was initiated in March 2019, based on OceanSITES and Argo user's manuals. This document is meant to be understood as purely format oriented; the scope is limited to just the syntax. Content, rules and relevant information is supported by VI. REFERENCES. Note on versions It is used Semantic Versioning (https://semver.org/) given a version number MAJOR.MINOR.PATCH, increment the: ● MAJOR version when you make incompatible API changes ● MINOR version when you add functionality in a backwards compatible manner ● PATCH version when you make backwards compatible bug fixes Additional labels for pre-release and build metadata are available as extensions to the MAJOR.MINOR.PATCH format. Note on updates In order to assure the stability of the format version, a maximum of one new minor version will be released every 6 months and a major version every 2 years, only when required.