A separate ISBN must be assigned to every title, or edition of a title by each publisher, but NOT to an unchanged impression or unchanged reprint of the same title in the same format by the same publisher. Revised editions require a new ISBN. A price change does not call for a new ISBN. Changes of the format induce a new ISBN. The same title being published in a series and individually is treated as two different editions.
A separate ISBN must be assigned to a facsimile reprint produced by a different publisher.
Publications in different product forms
Different product forms of a publication (e.g., hardback, paperback, Braille, audiobook, online electronic publication) require separate ISBNs. Where electronic publications are made available in different formats (e.g. .lit, .pdf, .html, .pdb) each separately available format shall be assigned a unique ISBN.
If a publication appears in loose-leaf form an ISBN is assigned to identify an edition at a given time. Individual issues of additions or replacement sheets will also be given an ISBN, when they are separately stocked.
An ISBN must be assigned to the whole set of volumes of a multi-volume work; also, if individual volumes of the set are sold separately, each volume must be assigned its own ISBN. Thus the individual processing and sale of single volumes is made possible. Even when multi-volume works are only sold as a set, the assignment of ISBN to each volume is advisable: It facilitates the handling of returns (damaged volumes) and the processing of shipments when not all volumes are published or distributed at the same time.