The IUPAC's rules for naming chemical compounds are written in a series of books. The system for naming organic compounds is written in the "Blue Book". The system for naming inorganic compounds is written in the "Red Book". A third book, called the "Green Book", gives recommendations about the use of symbols for physical quantities. A fourth book, the "Gold Book", contains the definitions of many of the technical terms used in chemistry. Similar books exist for biochemistry, analytical chemistry, macromolecular chemistry, and clinical chemistry. The books do not cover everything, however. Shorter recommendations for specific circumstances are published sometimes in the journal "Pure and Applied Chemistry".