Under Art. 82 EPC, the European patent application must relate to one invention only or to a group of inventions so linked as to form a single general inventive concept. R. 44(1) EPC (cf. R. 30 EPC 1973) gives an interpretation of the concept of unity of invention where a group of inventions is claimed. For international applications the corresponding provisions are Art. 3(4)(iii) PCT and in particular R. 13 PCT.
As stated in T 501/91, the main purpose of Art. 82 EPC is to prevent several unrelated inventions from being dealt with in a single patent application in order to save fees. It also helps to ensure that claimed and granted intellectual property rights are correctly classified. Moreover, it is in the interests of a rational examination procedure that unrelated subject-matter is not lumped together in a single patent application, while related subject-matter should not be needlessly split up (see T 110/82, OJ 1983, 274).
Procedural aspects of the assessment of unity, including the payment of further search fees, are governed by R. 64 and 164 EPC (cf. Art. 17(3)(a), R. 40 PCT for the ISA, and Art. 34(3)(a), R. 68 PCT for the IPEA).
Protests under the PCT in respect of additional fees paid following a non-unity objection by the EPO acting as ISA (R. 40 PCT) or as IPEA (R. 68 PCT) were previously decided on by the boards of appeal (Art. 154(3) and 155(3) EPC 1973), but are now decided on by review panels of the EPO (R. 158(3) EPC, decision of the President of the EPO, OJ 2015, A59; for the interim procedure see notice of 1 March 2005, OJ 2005, 226). The boards' competence to consider unity in the context of European applications remains unaffected. Given the harmonisation of the definitions concerning unity of invention in R. 13 PCT and Art. 82, R. 44 EPC, the criteria for unity in both systems are the same. Therefore, board decisions rendered according to the former PCT protest procedures ("W" cases) continue to be of interest for the consideration of unity in European applications and so many have been included in this chapter.
The Guidelines for Examination in the EPO (March 2022 version) deal with unity of invention at the search stage in Part B‑VII, unity as a procedural aspect of substantive examination in Part C‑III, 3, and unity as a requirement of the European patent application in Part F‑V. For international applications see especially Chapter GL/ISPE 10 of the PCT International Search and Preliminary Examination Guidelines, as in force from 1.3.2022, and the Guidelines for Search and Examination at the EPO as a PCT Authority, B‑VII, C‑V and F‑V – March 2022 version.