ACM's first classification system for the computing field was published in 1964. Then, in 1982, the ACM published an entirely new system. New versions based on the 1982 system followed, in 1983, 1987, 1991, and 1998. The 2012 scheme utilizes a new poly-hierarchical structure and a more in-depth approach than the 1998 version. It no longer uses the letter-and-number coding of the previous versions. The old scheme has been mapped to the new, and both the 1998 and 2012 terms are available on Citation Pages of all indexed articles in the ACM Digital Library.

• the 2012 system
• the 1998 system
• the 1991 system
• the 1964 system

Tools to help authors apply the 2012 CCS categories and concepts are being built. A new set of instructions will be issued in early 2013. Until then, authors please continue using the 1998 categories, following these instructions on how to classify your work: How to Classify Works Using ACM's Computing Classification System.