Some publishers issue separate recurring publications to complement, bring up-to-date, or provide special features to an existing serial. These publications typically have a formal relationship with the main work in that they are published or distributed by the same publisher and are usually covered by the same subscription. Some supplements are given in the title " supplement", others have unique titles but indicate that they are issued as a supplement to the main work. Some supplements to serials are themselves serials, others are not. Supplements can be issued frequently or infrequently; regularly or irregularly. Supplements may carry designations that may or may not be a part of the designation of the main work. Some supplements carry only a date.

See also:

17.4. Serial supplements