The Universal Decimal Classification system is widely used throughout the world for the arrangement of books in libraries and for the indexing of papers and reports as an aid to the retrieval of information. It is a comprehensive and language-independent system. The classification for astronomy and related topics (UDC 52) is used by many persons whose main interests are outside astronomy as well as by astronomical specialists. It is important that the classification be kept up to date, but the revision of UDC 52 is now overdue, as the last major revision was made in 1975 and published in 1977. It is clearly the responsibility of IAU Commission 5 to provide expert advice to the International Federation for Information and Documentation (FID) on the revision. Persons who are willing to participate in the work of revision are invited to write to the author, who is the current chairman of the relevant revision committee.