The mmCIF file format (macromolecular Crystallographic Information) was developed under the auspices of the International Union of Crystallography (IUCr) to extend the Crystallographic Information File (CIF) data representation used for describing small molecule structures and associated diffraction experiments.

• Large structures (containing >62 chains and/or 99999 ATOM records) that cannot be fully represented in the PDB file format are available in the PDB archive as single PDBx/mmCIF files.
• PDBx/mmCIF file format provides richer data annotation
• PDBx/mmCIF became the standard PDB archive format in 2014. Since 2016 the PDB File Format is no longer being modified or extended to support new content.