Divisional patent application
A divisional patent application (sometimes referred to as a divisional application or simply a divisional) is a type of patent application which contains matter from a previously filed application (the so-called parent application). Whilst a divisional application is filed later than the parent application, it may retain its parent's filing date, and will generally claim the same priority.
Divisional applications are generally used in cases where the parent application may lack unity of invention; that is, the parent application describes more than one invention and the applicant is required to split the parent into one or more divisional applications each claiming only a single invention. The ability to file divisional applications in cases of lack of unity of invention is required by Article 4G of the Paris Convention.
Practice by jurisdiction
The practice and procedure of filing a divisional patent application varies from jurisdiction to jurisdiction. In most countries, the filing of divisional applications is possible at least as long as the parent patent applications is pending. With a decision of the Administrative Council of the European Patent Organisation of October 16, 2013, the European Patent Office rules will again be in line with the current practice before the patent offices in the U.S., Germany and Japan.
European Patent Convention
Before the European Patent Office (EPO), divisional applications can be filed under Article 76 EPC. A European divisional application is a new application which is separate and independent from the parent application, unless specific provisions in the European Patent Convention (EPC) require something different. 
- "The procedure concerning the divisional application is in principle independent from the procedure concerning the parent application and the divisional application is treated as a new application.... Although there are some connections between the two procedures (e.g. concerning time limits), actions (or omissions) occurring in the procedure concerning the parent application after the filing of the divisional application should not influence the procedure concerning the latter...." 
The practice relating to the filing of divisional applications under the EPC was clarified by the Enlarged Board of Appeal of the EPO in June 2007. The Board held that a divisional application which on filing contained subject-matter extending beyond the content of the earlier application as filed could be amended later to remove the deficiency, even at a time when the earlier application is no longer pending.
- "Paris Convention for the Protection of Industrial Property". WIPO. Retrieved 2006-07-24.
- "Decision of the Administrative Council of 16 October 2013 amending Rules 36, 38 and 135 of the Implementing Regulations to the European Patent Convention (CA/D 15/13)". epo.org. European Patent Office. 24 October 2013. Retrieved 26 October 2013.
- Decision G 1/05 of the Enlarged Board of Appeal of the EPO[permanent dead link], Reasons 3.1 and 8.1.
- Opinion G 4/98 in point 5 of the Reasons, cited in decision G 1/05 of the Enlarged Board of Appeal of the EPO[permanent dead link], Reasons 8.1.
- Decisions G 1/05 and G 1/06 of the Enlarged Board of Appeal of the EPO.