The Scott catalogue of postage stamps, published by Scott Publishing Company, now a subsidiary of Amos Media, is updated annually and lists all the stamps of the world that its editors recognize as issued for postal purposes. It is published in fourteen large volumes that include twelve 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. The numbering system used by Scott to identify stamps is dominant among stamp collectors in the United States, Canada and Mexico.

A postage stamp is a small piece of paper issued by a post office, postal administration, or other authorized vendors to customers who pay postage. Then the stamp is affixed to the face or address-side of any item of mail—an envelope or other postal cover —which they wish to send. The item is then processed by the postal system, where a postmark or cancellation mark—in modern usage indicating date and point of origin of mailing—is applied to the stamp and its left and right sides to prevent its reuse. Next the item is delivered to its addressee.