A divisional application is a new application which is separate and independent from the earlier application. Therefore, divisional applications are to be treated in the same manner as ordinary applications and are subject to the same requirements, unless specific provisions of the EPC require something different (see G 1/05 date: 2007-06-28, OJ 2008, 271). The most important provisions on European divisional applications are Art. 76 EPC and R. 36 EPC (R. 25 EPC 1973).
According to Art. 76(1), second sentence, EPC, the divisional application may be filed only in respect of subject-matter which does not extend beyond the content of the earlier application as filed. The divisional application is accorded the same filing date as the parent (earlier) application and benefits from any right of priority of the parent (earlier) application in respect of the subject-matter contained in the divisional application. When determining whether the subject matter of a divisional application extends beyond the content of the earlier application as filed (Art. 76(1), second sentence, EPC) exactly the same principles are to be applied as for extension of subject-matter under Art. 123(2) EPC (G 1/05 date: 2007-06-28; see in this chapter II.F.2.1.).
Divisional applications may be amended like any other application. If a divisional application is amended, it must meet the requirements of both Art. 76(1) EPC and Art. 123(2) EPC, so as to preclude the introduction of new subject-matter into the proceedings (see in this chapter II.F.2.2.).
A divisional application (of whatever generation) can be the "earlier application" within the meaning of Art. 76(1) EPC for a further divisional (G 1/06, OJ 2008, 307). According to R. 36(1) EPC the earlier application must still be pending (see in this chapter II.F.3.5.).
It is a ground of opposition and a ground of revocation if the subject-matter of a patent granted on a divisional application extends beyond the content of the earlier application as filed, see Art. 100(c), 138(1)(c) EPC.
The question whether a European divisional application may anticipate its parent ("poisonous divisional") is treated in the context of partial priority in T 557/13 date: 2017-07-28 (OJ 2016, A87; referral G 1/15). For a summary of G 1/15 (OJ 2017, A82), see in chapter II.D.5.3. "Multiple priorities or partial priority for one claim".