The issue of when to use a separate eBook ISBNs continues to be an area of confusion for many publishers. Here are the simple facts about eBook ISBNs:

--The best practice within the industry is to provide a separate ISBN for each file type

--However: A separate ISBN is not compulsory

--Why provide separate ISBNs? Separate ISBNs are useful for reporting sales and managing multiple formats. This is most useful when there are large numbers of titles and formats.

ISBN types:

--Parent ISBN: All physical books carry a Parent ISBN. Where no physical title exists, the digital ISBN is used as the parent

--PDF ISBN: Necessary in order to distribute PDF files. Highly recommended to supply PDFs thousands of library outlets use this file type

--ePub ISBN: The digital ISBN for ePub files, which are the most widely accepted by retailers

--Mobi ISBN: Specific to mobi files for Amazon. Can be the same as ePub. A separate ISBN is best practice, but this shouldn’t been seen as a barrier to distributing mobi files. Amazon continue to contribute the largest proportion of sales

Multiple ISBNs and DRM

According to the International ISBN Agency, “If the different versions use the same DRM software (e.g. Adobe ACS4) with substantially the same settings and are interoperable on different devices or software, then a single ISBN should be used. If, however, the same DRM software is used on two versions but with significantly different settings (e.g. one allows printing but the other does not) then each version should have its own separate ISBNs. If proprietary DRM is used that ties a version to a specific platform, device or software then, if ISBNs are assigned (see 6 below), separate ISBNs should be used for each such version."

How can all the different versions of an eBook be linked together?

The ISTC (International Standard Text Code) is a new ISO identifier that identifies the underlying textual content of the book and is therefore shared by all digital and physical manifestations of the same title. The assignment of ISTCs would facilitate the linking of all versions and, with the addition of a filtering element such as product form, could also be used to link all e-book versions. Some systems already use an internal work identifier to provide this functionality but this cannot be used in the supply chain. Further information including ISBN Guidelines are available from the International ISBN Agency at http://www.isbn-international.org/ Further information on ISTC is available at http://www.istc-international.org