For example, German patent law already prevents double patenting by an earlier application and an application claiming its priority at an early stage of the proceedings, since according to § 40 (5) PatG the earlier application from which priority is claimed is deemed withdrawn already with the declaration of priority.
On the other hand, US Patent Law knows two types of double patenting objections to be risen during the proceedings up to grant. One is the non-statutory (case law) "obviousness type double patenting objection", which is based on the judicial doctrine according to which a prolongation of the patent term has to be prevented by prohibiting claims in another patent that are obvious variations on claims of the granted patent. The other is the "same invention type double patenting objection" based on 35 U.S.C. Sec. 101, which states that an inventor "may obtain a [i.e. one] patent" only. While the former can be overcome by a terminal disclaimer declaration which disclaims the term of the later-issuing patent that extends beyond the term of the earlier patent, the latter objection may be tackled by joining all claims that relate to the same invention in one single application.
In Europe, the EPO Board of Appeal held in May 2000 in case T 587/98 that
there is no provision in the EPC (not even implicitly) which prohibits in a divisional application an independent claim which is related to an independent claim in the parent application in such a way that the parent claim includes all the features of the divisional claim combined with an additional feature.In June 2007, the Enlarged Board of Appeal accepted in cases G 1/05 and G 1/06 that
the principle of prohibition of double patenting exists on the basis that an applicant has no legitimate interest in proceedings leading to the grant of a second patent for the same subject-matter if he already possesses one granted patent therefor.The Enlarged Board therefore accepted the practice of the EPO "that amendments to a divisional application are objected to and refused when the amended divisional application claims the same subject-matter as a pending parent application or a granted parent patent."
In July 2007, case T 307/03 explicitly disagreed with the apparent conclusion of earlier T 587/98 that there would be no basis in the EPC for prohibiting conflicting claims and thus followed the Enlarged Board of Appeal. It was concluded in T 307/03 that a patent cannot be granted on a divisional application claiming the same subject-matter as the parent application, even not if the claims of the divisional application are broader. The prohibition of double patenting was notably derived from Article 60 EPC, according to which the "right to a European patent shall belong to the inventor or his successor in title":
[once] a patent has been granted to the inventor (or his successor in title) this right to a patent has been exhausted, and the European Patent Office is entitled to refuse to grant a further patent to the inventor (or his successor in title) for the subject-matter for which he has already been granted a patent.In November 2008, the Board of Appeal held in T 1391/07 that a double patenting objection did not arise when the claims of two applications only overlap. In other words, when there is a partial overlap in the respective scopes of protection,
there is at least one technical feature in each of divisional claim 1 and parent claim 1 clearly distinguishing the subject-matter of the respective claim from that of the other one of the claims, and that these distinguishing features are such that the scope of protection sought by the invention claimed in the divisional application is notionally different from the scope of protection conferred by claim 1 of the granted parent patent.In the present case T 1423/07 the Examining Divison referred to the Guidelines for Examination according to which patents in the name of the same applicant must not contain claims of substantially identical scope. In fact, under section C-IV, 7.4 it reads that the EPC does not deal explicitly with the case of co-pending European applications of the same effective date but, however,
it is an accepted principle in most patent systems that two patents cannot be granted to the same applicant for one invention. It is permissible to allow an applicant to proceed with two applications having the same description where the claims are quite distinct in scope and directed to different inventions. However, in the rare case in which there are two or more European applications from the same applicant definitively designating the same State or States (by confirming the designation through payment of the relevant designation fees) and the claims of those applications have the same filing or priority date and relate to the same invention (the claims conflicting in the manner explained in ), the applicant should be told that he must either amend one or more of the applications in such a manner that they no longer claim the same invention, or choose which one of those applications he wishes to proceed to grant.The Board of Appeal denied existence of "accepted principle in most patent systems" and disagreed the above-sketched Board of Appeal case law, since, firstly, the EPC does not contain an explicit provision prohibiting double patenting and, secondly, since most Contracting States have provisions prescribing that a national patent ceases to have effect in case of double patenting with a European patent, which are, however, not related to double patenting in the pre-grant stage. In fact, the Board did not find a principle of procedural law generally accepted in the Contracting States that the refusal of an application for double patenting is provided for.
In T 307/03 the ruling that a patent cannot be granted on a divisional application claiming the same subject-matter as the parent application was derived from Article 60 EPC, whereas the Board this time concluded that there is no way that Article 60 EPC could provide basis for refusing a European application under Article 97(2) EPC for double patenting. Contrary to T 307/03, the board in this case found that
the fact that the EPC does not contain any specific provisions relating to double patenting is decisive: in the absence of such provisions, a refusal of a European patent application for double patenting is not possible irrespective of whether or not double patenting is a rare occurrence.Also the situation in G 1/05 was considered different to that of the unterlying appeal, since in G 1/05 the parent and its divisional application had the same filing date, while in T 1423/07 the term of the patent to be granted on the second application is to be calculated from its own filing date and not from the filing date of the priority application. Thus, the applicant has a legitimate interest in obtaining longer protection based on his second application.