The Scott Catalogue of postage stamps, published by Scott Publishing Co, is updated annually and lists all the stamps of the entire world which its editors recognise as issued for postal purposes. It is published in eight large volumes that include six volumes containing all the countries of the world that have ever issued postage stamps, the United States Specialized Catalog, and the 1840-1940 Classic Specialized Catalogue (covering the world for the first 100 years that stamps were issued). The numbering system used by Scott to identify stamps is dominant among stamp collectors in the United States, Canada and Mexico. The Scott Catalogue is the leader in the stamp market and a must for all collectors and researchers.