The basic principle behind the requirement of unity is that a patent is granted for each invention separately, i.e. in order to proceed to grant, a European patent application is required to contain claims relating to one invention only (G 2/92, Reasons 2).

This requirement of unity is further justified by the principle of equal treatment of applicants: any applicant is entitled to the same rendered service against the paid fees, i.e. one search/examination against one search/examination fee.

Therefore at the search stage, if an application as filed is considered by the search division to relate to more than one invention, a search fee may be paid for each such invention, and the search report will be drawn up only in respect of inventions for which search fees have been paid. At the examination stage the applicant can select only one searched invention in each application to be examined for conformity with the patentability and other requirements of the EPC (see G 2/92, Reasons 2).[Rule 64; ]

Art. 82 and Rule 44 govern the application of the requirement of unity to European patent applications. This requirement is not applicable in opposition proceedings (G 1/91).

This chapter deals with the substantive aspects of the assessment of unity of invention (F‑V, 2 and F-V, 3), as well as some procedural aspects relating to lack of unity during search (F-V, 4) and lack of unity during substantive examination (F-V, 5). Aspects of unity of invention in the case of amended claims and Euro-PCT applications are dealt with in F-V, 6, and F-V, 7, respectively. Further aspects related to the procedural implementation of unity of invention in search and examination are to be found in chapters B‑VII and C‑III respectively.

Given the harmonisation of the definitions concerning unity of invention in Rules 13(1) PCT and Rule 13(2) PCT versus Art. 82 and Rule 44(1) respectively, the criteria for unity in both systems are the same. Hence, unity of invention is examined in search and substantive examination in both European and PCT procedures according to the same principles. This does not apply to the respective procedures themselves, where significant differences exist.[Art. 150(2); ]

Consequently, decisions of the boards of appeal rendered according to the former PCT protest procedures continue to be of interest for the consideration of unity in European applications.