Each year, Scott Publishing Company produces an updated Specialized Catalog of U.S. stamps. The Scott Catalog does not offer stamps for sale, but lists estimated values for each issue and identifies each with a "Scott Number." As new stamps are issued by the U.S., Postal Service, Scott assigns catalog numbers to them. Because the Scott catalog is a highly respected authority and because Scott Numbers were the first comprehensive identification system for stamps, nearly all stamp dealers, collectors, and even the U.S. Postal Service use Scott Numbers to identify U.S. stamps. Your Mystic catalogs and circulars list U.S. stamps by Scott Number. Most foreign stamps are also identified by Scott Catalog Numbers. Various countries around the world have their own catalogs. Great Britain uses Gibbons, Germany uses Michel, and France its Yvert. Italy's catalog is Bolaffi.