United States Government publications are classified by the Superintendent of Documents Classification System (SuDocs). This system was first used in the library of the Government Printing Office sometime around 1900. Over the past century, the SuDocs system has expanded as the size and scope of the federal government has grown.

SuDocs has proved to be an efficient method of classifying federal documents. It is based on groupings of publications by government author, including departments, bureaus and agencies. In these groupings, the organizational structure of the United States government is mirrored. That is, subordinate bureaus and divisions are grouped within and under the parent organization. 

Unlike the other major classification system found in the Library (the Library of Congress classification system), the SuDocs system does not lend itself well to being browsed by call number or shelf location. A given subject (for example, Food Stamps) can cross numerous different departments. This makes the use of special finding aids critically important, and the assistance provided by a Government Publications Reference Librarian invaluable. 

And since the SuDocs system reflects the specific organizational structure of the federal government, whenever the government is reorganized, the call numbers change to reflect this altered structure. Thus, some publications can be located in several different places on the shelves.

For assistance or further information, visit our Government Publications web pages.

The first letter/letters of a SuDocs number represents the government department or agency (parent organization) responsible for publication.  All letters and combinations of letters are used except for the letter Z. The letters X and Y are used for Congressional publications.

Example:

I for Interior Department

The letters are followed by a number representing the agency as a whole, or a subordinate office. This figure is followed by a period.

Examples:

I 19. for Geological Survey
I 28. for Bureau of Mines
I 29. for National Park Service

After the period, there is a number designating the series or category grouping of publications followed by a colon.

Example:

I 19.3: for Geological Survey  Bulletins

Sometimes there are related series to already existing series. In order to have these related series filed together, a slash prior to the colon is used to indicate the relationship.

Example:

I 19.3/3: for Geological Survey Water Resources Bulletin

The numbers after the colon represent individual publications in the series.

Example:

I 19.3/3:751 for bulletin 751

There are various sub member designations that give added information. Among these: Series Designations:

I 19.1 for Geological Survey Annual Reports

I 19.3 for Geological Survey Bulletins

I 19.1:985 for Geological Survey Annual Report 1985

I 1.94:7/Pt 2 for Water Resources Catalog Volume 7 Part 2

Follow these rules when looking for document call numbers on the shelf:

1. The arrangement is alphabetical letter by letter.  Filing follows a "nothing before something rule." For example, (Interior publications) files before ITC (International Trade Commission publications)
2. The number between the period and the colon is a whole number, not a decimal. Thus, the shelf order is:
   • I 19.1: =U.S. Geological Survey Annual Reports
   • I 19.3: =U.S. Geological Survey Bulletins
   • I 19.16: =U.S. Geological Survey Professional Papers
3. After the colon, new lines in the number are shown by slash marks (/).
4. Publications that differ in their classification number after the colon, the rule is DATE before LETTER before NUMBER before WORD. However, this does not apply to parts, volumes, sections, or revisions of the same publication.

Below is a list of properly ordered U.S. government publications.

• I 1.98:T 68
• I 1.98:T 68/decision
• I 1.98:T 68/draft
• I 19.1:989
• I 19.1:991
• I 19.2:M 86
• I 19.2:M 86/980
• I 19.2:M 86/2
• I 19.2:M 86/2/990
• I 19.3:1134
• I 19.3/3:657
• I 19.14:990
• I 19.14/4:987/5
• I 19.14/4:987/6

The Colorado classification system used to order this collection is similar to the U.S. Superintendent of Documents Classification system. In the Colorado State Publications Classification system, the initial letters of the call number indicate the issuing agency. The numbers following the initial letters indicate the primary division while numbers following a slash designate any further subdivision of the agency.

Colorado Department of Natural Resources and selected sub-agencies within the Department

• NR =all of the agencies and sub-agencies within the Department of Natural Resources
• NR 1. =Colorado. Dept. of Natural Resources
• NR 2. =Colorado. Soil Conservation Board
• NR 5. =Colorado. Division of Water Resources
• NR 12. =Colorado. Division of Minerals and Geology
• NR 12/20. =Colorado Geological Survey
• NR 12/40. =Colorado. Office of Mined Land Reclamation
• NR 12/60. =Colorado. Office of Active and Inactive Mines

• NR 1.1 =Colorado. Dept. of Natural Resources Annual Reports (usually followed by a date)
• NR 1.2 =Colorado. Dept. of Natural Resources General Publications (usually followed by a cutter number)
• NR 1.3 =Colorado. Dept. of Natural Resources Bulletins (usually numbered)

The Colorado state publications are filed by agency first, followed by the sub-agencies within the larger agency. Therefore a period, which separates the agency from the type of publication, precedes the slash which designates a sub-agency (i.e. NR 1.3 precedes NR 1/2). Like SuDocs, Colorado state publications follow the "nothing before something" rule, and DATE before LETTER before NUMBER before WORD rules. Below is a list of properly ordered Colorado state publications.

• NR 1.1/1992
• NR 1.3/13
• NR 2.2/L3
• NR 2.2/L3/1990
• NR 2/2.1/1989
• NR 3.1/1985
• NR 12.2/F34/1985
• NR 12.2/G87/1983
• NR 12/20.1/1988
• NR 12/20.2/P27/1991
• NR 12/20.13/1979