United States government documents are classified using the Superintendent of Documents (SuDocs) classification system. The classification system is based on the issuing agency, and is used only for United States government documents.

SuDocs numbers are alphanumeric: they are composed of letters, numbers, and punctuation marks.

In the SuDocs classification system, the call number is divided into two parts: the class stem is the part before the colon, and the individual book number is the part after the colon.

• Ex: J 24.2:Am 3
• J 24.2: is the class stem
• Am 3 is the individual book number

The first letter or letters in the class stem denotes the executive department or agency:

• J = Justice Department

The first number in the class stem represents the issuing bureau:

• J 24. = Drug Enforcement Administration (DEA)

The second number in the clas stem represents the publication series:

• J 24.2: = General Publications

Periods, slashes and colons separate each section of the call number. Documents are shelved alphabetically by the first letter(s) and then numerically, by each section:

• J 1.30:
• J 21.2:
• J 21.2/10:
• J 21.6/3:

All numbers are shelved as whole numbers, not decimals:

• J 26.2:
• J 26.8:
• J 26.30:

The individual book number may be represented by a year, a document number, or a Cutter number composed of letters and numbers:

• Year: J 26.1:2003 (Note: years before 2000 are represented without the 1 -- eg. 994=1994)
• Cutter number: J 24.2:Am 3
• Document number: J 32.10:410

Individual book numbers often are followed by a slash and a date, indicated another edition. These shelve in order after the first edition, but before the next individual book number:

• J 24.2:Am 3
• J 24.2:Am 3/2007
• J 24.2:An 1