Double patenting occurs when a person or company submits more than one application to a government office for a patent on a single invention. The purpose is to extend the duration of a patent. The typical term of a patent is 20 years. A patent protects an invention by prohibiting others from using, selling, or otherwise infringing upon it. Nations that grant patents do not favor double patenting.
Organizations or inventors attempt double patenting by filing multiple applications for a patent. In the U.S., for example, one method inventors try to use is a continuation application to extend the duration of a patent. This, however, is not the purpose of a continuation application. The purpose is to protect new improvements to an invention.
The policy behind granting patents is to encourage inventions. A patent allows an inventor to benefit from his invention exclusively for a set period. At the expiration of a patent, the public benefits by being able to use the invention freely, and society thereby benefits as a whole. An inventor thwarts the system by unfairly extending the duration of patent through double patenting.
Most countries that grant patents use double patenting as a basis to deny an application. For example, the U.S. Patent and Trademark Office (USPTO) will reject an application if it determines that it is from the same applicant and for the same invention. This is a rejection based upon statutory law which does not permit multiple patents for a single invention from the same inventor. Patent lawyers refer to this as same invention double patenting. In other words, an inventor is entitled to only one patent for one invention.
The USPTO may also reject a patent application based upon court precedents that prohibit double patenting. The court system has established that a second patent is invalid if it is an obvious variation of a patent, owned by the same inventor, or subject to assignment to the same person. Patent lawyers refer to this as obviousness type double patenting. This is an equitable remedy to prevent extending the duration of a patent.
It is possible for inventors to remedy the problem of double patenting. For instance, an inventor may modify the application for a patent or may also submit a terminal disclaimer which states that the duration of the second patent would not exceed the duration of the initial patent. There are other methods to overcome a rejection depending on the facts of each situation.