The printed U.S. Government publications we currently house are mostly kept in a separate section in the library, and are shelved using a special call number system: the SuDocs system, short for the Superintendent of Documents System. It is a system of letters, numbers, and punctuation (such as colons and slashes) unique to federal documents. Each call number starts with a letter(s) that indicates the issuing agency. Thus Agriculture Department documents start with the letter A, Defense with D, etc. There are, of course, exceptions: since the Commerce Department got C, Congress is filed under Y.