The European patent application shall relate to one invention only or to a group of inventions so linked as to form a single general inventive concept.

An initial opinion on whether the claims of an application fulfil the requirement of unity or not is formed by the search division (i.e. the search examiner). The applicant is informed if a lack of unity objection is raised at this stage and if additional search fees have to be paid to get more than the first invention searched.