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Non-patent literature (NPL)

The EPO's search documentation includes patent literature and any other printed or non-printed matter that may be technically relevant for the patent-granting procedure.


Non-patent literature is assigned NPL reference numbers. These have a format similar to patent publication numbers but, instead of a country code, the letters XP are used.


In Espacenet the bibliographic details of non-patent literature documents (XP documents) are only displayed if:


  • the XP documents have been classified using the Cooperative Patent Classification (CPC) or
  • they have been cited in a search report produced by the EPO.

The bibliographic data of a non-patent literature (XP) document shows the NPL reference number, the publication date, a classification (CPC) symbol (where applicable), the URL of the citation (where available) and an external disclaimer.


Clicking on this URL will open a new window to the external provider, who might have the complete information. However, the EPO has no control over these linked pages and it may happen that they lead to dead links.


Where available a DOI link has been added. A DOI (digital object identifier) is a permanent digital identifier given to an object to identify electronic intellectual property documents. The system, which defines permanent unique IDs for digital documents, is managed by the International DOI Foundation.


If you know a DOI corresponding to a non-patent literature document, you can retrieve the article just by inputting the field identifier "doi=" plus the DOI number in the Smart search mask.


Example: doi="10.1016/0167-8655(88)90080-3"


It is not possible either to retrieve an XP document by the name of the author or to limit a search to XP documents only.


XP numbers comprise the letters XP followed by a serial number (variable, maximum nine digits).


Examples: XP1, XP000123456


XP documents can be retrieved by entering the corresponding number in the Smart search mask.


For more information on Espacenet, see the following pages: