The UNSW Libraries use the Dewey Decimal Classification Scheme and the Moys Scheme (for Law material) to arrange books by subject area. Their use means that all books on the same subject will be shelved together.
The Library also uses letter prefixes with the call numbers from these schemes to determine the location of the books in the Special Libraries.

The word "decimal" refers to numbers that are based on 10 (ten). There are 10 basic categories in the system and each of those categories is further split into 10 categories.
Further information on the Dewey Decimal Classification Scheme is available from the OCLC Dewey site.