The date of filing of the European patent application shall be the date on which the requirements laid down in the Implementing Regulations are fulfilled (Art. 80 EPC, which is applicable to European patent applications filed on or after 13.12.2007). Detailed provisions concerning the requirements have been moved to the Implementing Regulations (R. 40 EPC). The requirements include:

- an indication that a European patent is sought;

- information identifying the applicant or allowing the applicant to be contacted (see in this chapter IV.A.5.2.);

- a description or reference to a previously filed application.

The patent application must be filed with the EPO or other competent authority in accordance with Art. 75(1) EPC.

If a date of filing cannot be accorded following the examination under Art. 90(1) EPC, the application is not dealt with as a European patent application (Art. 90(2) EPC).

According to G 2/95 (OJ 1996, 555), Art. 80 EPC 1973 stipulated the minimum requirements which had to be met in order for a filing date to be accorded. According to Art. 80(d) EPC 1973 (see now R. 40 EPC), the documents filed by the applicant had to contain a description and one or more claims (in accordance with Art. 14 EPC 1973, which was substantially amended in the EPC 2000). However, the description and claims did not have to comply with the other requirements of the EPC 1973. It was sufficient for the application documents to clearly contain a description and one or more claims. However, if they did not contain a description or claims, the requirements for according a filing date under Art. 80(d) EPC 1973 were not met and could not be created subsequently by way of a correction under R. 88 EPC 1973 (see now R. 139 EPC and this chapter IV.A.5.5.). If the application documents met the requirements of Art. 80 EPC 1973, the European patent application was accorded a filing date.

In J 18/86 (OJ 1988, 165) the board stated that under R. 24 EPC 1973 in conjunction with Art. 75(1)(b) EPC 1973 the date of filing of a European application was always the date on which the application documents were actually received, either by the EPO directly or by a competent national authority. Nothing in the EPC 1973 admitted of the possibility of applying a provision of any national law to the determination of the date of filing of a European patent application.

In J 4/87 (OJ 1988, 172), the board held that in the event of an unforeseeable postal delay causing non-compliance with a time limit, if R. 85(2) EPC 1973 (relating to general interruption or subsequent dislocation in the delivery of mail in a Contracting State) was not applicable so as to extend the time limit, the EPO had no discretion to extend it. Applying the principles set out in J 18/86 above, the date of filing was the actual date of receipt by the EPO or a competent national authority. See also J 13/05.

In J 12/05, the Legal Board, citing J 4/87 and J 18/86, held that the EPC did not permit backdating of the filing date. It went on to state that, even where the conditions for extending the priority period under either R. 84a EPC 1973 or R. 85 EPC 1973 were met, this did not result in a change of the actual filing date. Instead, there arose a legal fiction that the priority period had been observed, even though the filing date was actually later than that period's expiry date.

In T 382/94 (OJ 1998, 24), the claims and description had been filed in German, but the drawings contained text matter in English. The board held that the EPC 1973 did not make the accordance of a filing date dependent on any text matter in the drawings being in a language in accordance with Art. 14(1) or (2) EPC 1973. If the drawings were filed in full on the date of filing, they formed part of the application as filed, even if they contained text matter in an official language other than the language of proceedings. The language requirements for a European patent application were amended under the EPC 2000, see chapter III.F.1. "Language of filing and date of filing of a European patent application".

In J 1/12 the appellant had filed a European patent application with the UK Patent Office with the same documents as those underlying the later application before the EPO. The application in the UK never reached the EPO. The Legal Board therefore had to consider whether, contrary to Art. 80 EPC 1973, it was justified to assign the application the earlier filing date (Art. 75(1)(b) EPC 1973). Art. 77(2) EPC 1973 provides that European patent applications filed within the member states are to be forwarded to the EPO within six weeks after filing. Art. 77(5) EPC 1973 supplements this provision by providing that European patent applications which do not reach the EPO before the specified time limit are deemed to be withdrawn. It followed that the application filed with the UK Patent Office was deemed to have been withdrawn. No re-establishment of rights is provided for. In such a situation the legislator expressly provides in the last sentence of Art. 77(5) EPC 1973 for the refund of the filing, search and designation fees. In addition, Art. 135(1)(a) EPC 1973 and Art. 136(2) EPC 1973 provide facilities for a conversion of the lost European patent application into national patent applications. It followed that the legislator of the EPC clearly recognised the harsh consequences of Art. 77(5) EPC 1973 for an applicant. But, having recognised the problem, the legislator did not provide the applicant with any means to regain the lost application.