The requirement of unity of invention serves a regulatory function in the interest of an efficient procedure up to grant (T 110/82 and F‑V, 6). It would be unfair to regard as having unity of invention those applications which, because of their heterogeneous content, entail a far greater than average expense to process, especially in respect of search, since this expense must partly be borne by the fees levied for other applications. A further aspect is the requirement for ready comprehensibility of the application's subject-matter, which may be impaired by heterogeneous subject-matter.

On the other hand, the general purpose of dealing with interconnected substantive issues within a single procedure would not be achieved if provisions relating to unity of invention were applied too strictly. For this reason, interconnected matter must not be split up needlessly (see F‑V).

1.1 Partial European search report

1.2 Invitation to pay further search fees

1.3 Documents relevant only to other inventions

1.4 Assessment and possible review of the unity requirement