National Serials Data Program, Library of Congress
International Standard Serial Number (ISSN)

ISSN and the U.S. Postal Service

In 1977 the United States Postal Service printed a notice in the Federal Register proposing that publications mailed at what were then called second class rates would be required to print a six-digit USPS identification number. At the request of publishers who were already printing the ISSN, the Postal Service agreed to accept the ISSN as an identification number when assigned or confirmed by the National Serials Data Program (NSDP), the U.S. national center for ISSN.

General Information

There are two categories of USPS publications processed by NSDP: applications and reentries:


Publishers wishing to use periodicals mailing rates must submit an application to USPS via the postmaster at the office of mail entry. Consult the postmaster for appropriate rules and procedures. (A domestic mail manual is also available for download at the USPS business web pages: Business Mail 101.) The postal service forwards completed applications to NSDP, where some are selected for ISSN assignment. Processing time at NSDP is usually one to two weeks. A form letter is addressed to publishers of serials not selected for ISSN assignment explaining the non-selection.


Publishers who are already authorized to mail at periodicals rates, but who change their title, frequency, known office of publication, or place of entry must file a reentry form and pay a fee. Consult the postmaster at the office of mail entry for regulations and procedures to be followed. At NSDP, new ISSN are assigned to reentries as required.

How did the Postal Service become involved in the use of the ISSN?

The USPS needed to develop an identification number for publications mailed at periodicals rates because many serial titles are identical or similar, and as a result, change of address notices were often sent to the wrong publisher and erroneous revenue and cost data were collected. The ISSN was adopted by the USPS for use on many serials in lieu of the USPS publication number because of the communication between publishers, libraries, abstracting and indexing services, etc. An obvious benefit to publishers is being spared the added cost and inconvenience of displaying two identification numbers on the same publication.

What is NSDP's purpose in processing USPS titles?

NSDP has several purposes in processing USPS titles: to confirm existing ISSN to the USPS so that publishers will not have to print two separate identification numbers; to aid in the identification and bibliographic control of U.S. serials by selecting for new assignments those titles most likely to be included in large files of serials such as those maintained by libraries, subscription agents, or abstracting and indexing services; and to monitor titles with existing assignments so as to catch misprinting of the ISSN and to catch title changes.

Does NSDP assign ISSN to all USPS applications?

It has never been NSDP's intention to assign ISSN to all of the titles mailed at periodicals rates, nor is that something USPS needs. The USPS file of periodicals titles includes many titles for which ISSN would be of marginal use: e.g., local church bulletins, newsletters of local fraternal and civic organizations, etc. For these, NSDP reports "NO ISSN ASSIGNED" to the USPS. However, it will assign ISSN to these titles if the publisher contacts our office directly. The USPS has its own identification number, a six-digit number that it assigns to all titles. In cases where NSDP has not assigned an ISSN, the publisher is required to print the USPS number. Both the USPS number and the ISSN, if assigned, are entered in the USPS database.

Is it necessary to get an ISSN before applying to mail at periodicals rates?

No, it is not necessary to have any identification number when an application is submitted (although many serials already do have an ISSN at that point). If an ISSN is assigned, it is reported to the appropriate Rates & Classification Service Center (RCSC), then to the postmaster at the post office of mail entry, who in turn reports the ISSN to the publisher as part of the periodicals rates authorization. Because this "indirect" notification can take some time, publishers are encouraged to apply directly to NSDP for an ISSN as early in your publication's history as possible--preferably before the first issue is published.

Can I use the ISSN immediately upon assignment by NSDP or must I wait until officially notified by the U.S. Postal Service?

You may begin printing the ISSN immediately, once notified of the number directly by NSDP and in advance of authorization to mail at periodicals rates.

Where should the ISSN be printed on a title mailed at periodicals rates?

NSDP's preferred printing location of the ISSN is the upper right corner of the front/cover page. However, for compliance with USPS regulations, the ISSN must be printed in the ID statement of the publication following the title. Consult with your postmaster for authoritative guidance on ISSN printing requirements for publications authorized for mailing at periodicals rates.

Is there a charge for the number?

No. Assignment of the ISSN is free and there is no charge associated with its use.

If I have both a USPS number and an ISSN for my publication, which number should I use?

In order to fulfill mailing requirements, a publication must carry the identification number authorized by the Postal Service. This will be either the ISSN or the USPS number. There are some publications to which ISSN is assigned after the USPS number has been reported to the publisher as the authorized identification number. For these publications, the ISSN is reported to the Postal Service, which instructs the local postmaster to report the ISSN to the publisher and requires the substitution of the ISSN for the USPS number.

Under rare circumstances the USPS will authorize as a single publication (with a single USPS number) what NSDP's rules define as separate publications to which individual ISSN must be assigned (e.g., multiple language or geographic editions, supplements, and buying guides. In these cases, the ISSN is not reported to the Postal Service and the USPS number will be the authorized number. Publishers who wish to print the ISSN in addition to the USPS number on such publications are encouraged to do so, but should print the ISSN in a location other than the USPS ID statement.

Can foreign publications be assigned ISSN?

Yes, but NSDP cannot assign ISSN to most foreign publications because it is responsible for only those ISSN for titles published in the United States. National centers have been established throughout the world to assign ISSN to publications of their respective countries. However, if a foreign publisher is printing an ISSN assigned by a foreign center, the ISSN will be reported by NSDP to the USPS for use as the identification number for periodicals mailing rates. Foreign publishers who wish to obtain ISSN should contact their country's International Serials Data System center, which is usually located in the national library. Complete information about the national centers may be found at the international ISSN web site: Or, you may write to the international center:

ISSN International Centre

20, rue Bachaumont

75002 Paris France

Email: [email protected]

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Library of Congress Help Desk ( February 19, 2010 )