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What are Terminal Disclaimers in US patent system, and how are they used?

When one patent already exists and a second patent is so similar to it that a terminal disclaimer has to be filed by the inventor, why bother granting the second patent?

This seems to violate the concept of a single patent for a single invention (35 USC 101).

It also gives the inventor the ability to ask for additional royalties in case of infringement, because there are multiple patents in play.

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A Terminal Disclaimer is a written statement by a patent owner stating that the owner has disclaimed, or renounced legal claim to, a period of a later-issued patent that would extend beyond the expiration of an earlier-issued patent. The terminal disclaimer avoids one type of double patenting rejection as long as both the patents are commonly owned.

There are two types of double patenting rejections.

First, there is statutory double patenting (covered under 35 USC 101), which is trying to get a patent for an identical invention to that claimed in another patent. It is not allowed under 35 USC 101.

Second, there is non-statutory (or obviousness type) double patenting, which is trying to get a patent that, while not identical, would be obvious in view of another patent. This type of double patenting is judicially created, and can be overcome by filing a terminal disclaimer.

The idea behind the terminal disclaimer is to prevent a patent owner from effectively extending the life of a patent by filing multiple applications with claims only differing a little from the first one.

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  • Thanks for Clarification regarding the double Patenting types. However, I have more basic doubt that if we have already detected that the inventor is trying to cover the same invention just by making a little difference in claims. Then why not to directly reject the patent application? – Sameer Sharma Jun 30 '16 at 12:10
  • I won't go into the legal technicalities, but there are scenarios where a patent applicant's previous applications are not considered as prior art for a later application by the applicant. Roughly, if the inventor hasn't publicly disclosed an invention and the corresponding application has not yet been published, then that application may not be available as prior art against a later-filed application. In such a case, the patent examiner may still be able to make a double patenting rejection. – Aldo Jul 20 '16 at 18:56

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