First, consider what you have in hand. Do you have a main work with accompanying material or do you have two independent works that could be cataloged separately? In the first situation you need to ask what is the main work and what is the accompanying material. Frequently, accompanying material is in a different physical format. While a hard copy (paper) item is often the main work, there are other situations in which the main work is the microfiche or CD-ROM and the paper is merely a guide or index to it.

According to LCRI 1.5E1, treat an item as accompanying material when it is issued at the same time by the same publisher and author, and when it has a general title or is otherwise dependent on the main work. Supplements and indexes may be cataloged separately or mentioned in a note but are never recorded as accompanying material.

Once you have determined what you have in hand, decide how to describe it. As with the illustration statement, consider the entire serial. Will each issue be likely to contain such material or is this more likely a one-time occurrence? If the latter is true, a note in the record is more appropriate (AACR2 12.5E1).

See also:

11.4. Accompanying material