Chemical registries--in the fourth decade of service.

Methods for precise yet usable descriptions of virtually any topic are essential, especially for identification of chemical compounds and materials. Systematic nomenclature and precise chemical structures, if known, are the ultimate in description of chemical compounds. However, there has always been a pervasive need for brief, yet precise methods to register chemical compounds for use in both indexing and retrieval of additional information. The most predominant chemical registration system is the Chemical Abstracts Service (CAS) Registry System, begun in 1965. The history and use of this system will be described, and its importance to a number of disciplines, not just chemistry, will be described.