CIF format
The Crystallographic Information File (CIF) Format
The official IUCr CIF site at :
http://www.iucr.ac.uk/iucr-top/cif/home.html
The following general information on the CIF file format is available here:
Universal Archive file for Crystallography
The CIF Syntax
IUCr Policy on the CIF
CHECKCIF and PRINTCIF services