4. Structure of ISBN

An ISBN always consists of ten digits preceded by the letters ISBN.
Note: In countries where the Latin alphabet is not used, an abbreviation in the characters of the local script may be used in addition to the Latin letters ISBN.

The ten-digit number is divided into four parts of variable length, which must be separated clearly by hyphens or spaces⁵:

ISBN 0 571 08989 5

or

ISBN 90-70002-04-3

Note: Experience suggests that hyphens are preferable to spaces.

The number of digits in the first three parts of the ISBN (group identifier, publisher identifier, title identifier) varies. The number of digits in the group number and in the publisher identifier is determined by the quantity of titles planned to be produced by the publisher or publisher group. Publishers or publisher groups with large title outputs are represented by fewer digits.

4.1. Group identifier

The first part of the ISBN identifies a country, area or language area participating in the ISBN system. Some members form language areas (e.g. group number 3 = German language group) or regional units (e.g. South Pacific = group number 982). A group identifier may consist of up to 5 digits.

Example: ISBN 90- ...

All group identifiers are allocated by the International ISBN Agency in Berlin.

4.2. Publisher identifier

The second part of the ISBN identifies a particular publisher within a group. The publisher identifier usually indicates the exact identification of the publishing house and its address. If publishers exhaust their initial contingent of title numbers, they may be allocated an additional publisher identifier. The publisher identifier may comprise up to seven digits.

Publisher identifiers are assigned by the ISBN group agency responsible for the management of the ISBN system within the country, area or language area where the publisher is officially based.

Example: ISBN 90-70002- ...

4.3. Title identifier

The third part of the ISBN identifies a specific edition of a publication of a specific publisher. A title identifier may consist of up to six digits. As an ISBN must always have ten digits, blank digits are represented by leading zeros.

Example: ISBN 90-70002-04- ...

4.4. Check digit

The check digit is the last digit of an ISBN. It is calculated on a modulus 11 with weights 10-2, using X in lieu of 10 where ten would occur as a check digit.

This means that each of the first nine digits of the ISBN – excluding the check digit itself – is multiplied by a number ranging from 10 to 2 and that the resulting sum of the products, plus the check digit, must be divisible by 11 without a remainder.

For example   ISBN 0-8436-1072-7:

4.5. Distribution of ranges

The number of digits in each of the identifying parts 1, 2 and 3 is variable, although the total sum of digits contained in these parts is always 9. These nine digits, together with the check digit, make up the ten-digit ISBN.

The number of digits in the group identifier will vary according to the output of books in a group. Thus, groups with an expected large output, will receive numbers of one or two digits and publishers with an expected large output will get numbers of two or three digits.

For ease of reading, the four parts of the ISBN are divided by spaces or hyphens.

The generation of hyphens at output by programming helps reduce work at input. It reduces the number of characters, eliminates manual checking of hyphenation, and insures accuracy of format in all ISBN listings and publications.

The position of the hyphens is determined by the publisher identifier ranges established by each group agency in accordance with the book industry needs. The knowledge of the prefix ranges for each country or group of countries is necessary to develop the hyphenation output program.

For example, the publisher identifier ranges of group number 0 in the English language group (Australia, English speaking Canada, Ireland, New Zealand, Puerto Rico, South Africa, Swaziland, United Kingdom, United States, and Zimbabwe) are as follows:

00 - 19
200 - 699
7000 - 8499
 85000 - 89999
900000 - 949999
9500000 - 9999999

The following table is an example of the range distribution of publisher identifiers. Assuming a group identifier of one digit only, the publisher identifier ranges might be as shown in the left-hand column and the title identifiers as shown in the right-hand column.

⁵ For purposes of data processing the 10-digit string is used without hyphens or spaces. Interpretation and human legible display is effectuated by means of the tables of group numbers and publisher identifier ranges.