SuDoc numbers are assigned by the Government Printing Office to materials published by federal agencies and distributed to Federal Depository Libraries in paper, microfiche, and CD/DVD formats.  NUL has been a depository library for more than 100 years and receives approximately 75% of the materials made available to depository libraries.

SuDoc numbers organize materials by the publishing agency, not by subject as in Dewey or LC.  Usually, but not always, the name of the agency provides the first letter(s) of the SuDoc call number.  

A few examples (to see a complete, current list):

There is a variety of punctuation used in SuDoc numbers.  You will see periods (.) colons (:) slashes (/) and dashes (-). However all numbers that you see are whole numbers, not decimals, and should be filed in whole number order, wherever they appear in the call number.

SuDoc numbers are made up of the STEM (all the letters/numbers/punctuation BEFORE the colon) and the SUFFIX (everything that FOLLOWS the colon).

SuDoc classes are arranged alphabetically based on the leading letter(s) in the stem.  SuDoc classes file alphabetically no matter how many letters are used (ex. L comes before LC;  N comes before NAS which comes before NS). 

The number in the stem between the period and colon is a whole number (ex. HS 1.2: comes before HS 1.15:).

Both before and after the colon, an empty space will file before a space that has a letter or number (i.e. “nothing” before “something”).