The CIF restraints and constraints dictionary (restrCIF) contains the CIF data names and associated definitions used for recording the restraints and constraints that were applied to the parameters of a structural model during the final refinement of a structure determination. They are agnostic with regard to the refinement method used, and so are not suitable for use as instructions to a refinement program. The specific classes of restraint and constraint included are: geometry parameters (bonds, angles, torsions) restrained to a particular value; geometry parameters of different groups of atoms restrained to be equal; planarity restraints; non-bumping restraints; rigid-body constraints; restraints on atomic displacement parameters. Arbitrary atom parameters can be restrained to a specified value, and a general field can be used to describe restraints or constraints that cannot be described by the other items in the dictionary.