References in European patent applications to other documents may relate either to the background art or to part of the disclosure of the invention.

Where the reference document relates to the background art, it may be in the application as originally filed or introduced at a later date (see F‑II, 4.3 and F-II, 4.4, and H‑IV, 2.2.6).

Where the reference document relates directly to the disclosure of the invention (e.g. details of one of the components of a claimed apparatus), then the examining division first considers whether knowing what is in the reference document is in fact essential for carrying out the invention as meant by Art. 83.

If not essential, the usual expression "which is hereby incorporated by reference", or any expression of the same kind, needs to be deleted from the description.

If matter in the document referred to is essential to satisfy the requirements of Art. 83, the examining division requires the deletion of the above-mentioned expression and that, instead, the matter is expressly incorporated into the description, because the patent specification must, regarding the essential features of the invention, be self-contained, i.e. capable of being understood without reference to any other document. Furthermore, documents are not part of the text to be translated pursuant to Art. 65 (T 276/99).[Art. 65; ]

Such incorporation of essential matter or essential features is, however, subject to the restrictions set out in H‑IV, 2.2.1. It may be that the search division has requested the applicant to furnish the document referred to, in order to be able to carry out a meaningful search (see B‑IV, 1.3).

If, for the disclosure of the invention, a document is referred to in an application as originally filed, the relevant content of the reference document is to be considered as forming part of the content of the application for the purpose of citing the application under Art. 54(3) against later applications. For reference documents not available to the public before the filing date of the application this applies only if the conditions set out hereto in H‑IV, 2.2.1, are fulfilled.

Because of this effect under Art. 54(3), it is very important that, where a reference is directed only to a particular part of the document referred to, that part needs to be clearly identified in the reference.