In files containing CMIP model-simulation output, global attributes are used to describe the source of the data, the imposed experiment conditions, the contents of the file, licensing restrictions, and other information useful to those analyzing the data. Here, we define the global attributes that should appear in CMIP6 files (some are required, others optional), along with the so-called CMIP6 “data reference syntax” (DRS). The subset of global attributes that define the DRS is used in constructing the directory structure and file names found in the CMIP6 archive, and also to construct URLs leading to further information about the simulations and in populating search facets.