Serials are publications issued in parts over an indefinite period of time.
They include continuing series of monographic publications, regular and irregular scholarly and professional journals, magazines of interest to particular groups or to the general public, and newspapers. Serials are bibliographically complex since they often merge with each other, change title, format, arrangement, periodicity, etc. Consequently, an understanding of the publishing history of serials and of their formats is very useful for bibliographic work. Russian and Soviet serial titles have been listed comprehensively in bibliographies, but indexes to their contents are very selective. This applies also to the national bibliography series of indexes for journals, newspapers, and reviews.