Patent Interference - What Is It?

Patent Interference is defined as a contest between an application and either another application or a patent. An interference is declared to ascertain priority; basically, who came up with the invention first., as a patent can only be granted to one person.  If two or more applications are filed by different inventors claiming substantially the same patentable invention, a proceeding known as an “interference” is instituted by the United States Patent and Trademark Office, USPTO, to determine who is the first inventor and entitled to the patent. 

Interference proceedings may also be instituted between an application and a patent already issued, assuming the patent has not been issued, nor the application published, for more than one year prior to the filing of the conflicting application, and also provided the conflicting application is not barred from being patentable for some other reason.

Patent Interference is rare; however, when it occurs, an examiner with the USPTO suggests an interference to the Board.  A panel of members will then review and provide a final judgement on the priority of the interference.  The final outcome of the inventor who proves to be the first to conceive the invention AND the first to reduce it to practice, will be held to be the prior inventor.  It is important to note, this decision can be appealed.


If a patent interference is declared, each party to the proceeding (a legal process to help decide ownership) must submit evidence of facts proving when the invention was made. Proof of evidence may include: a good dated, signed, and witnessed notebook. 

Providing solid evidence assists the USPTO panel to determine priority.  Proving the various facts and circumstances concerning the making of the invention during an interference, is key. It is important to note, if no evidence is submitted, a party is restricted to the date of filing the application as his/her earliest date, which may hurt the case findings.

A board, consisting of three administrative patent judges, reviews the evidence to make a final decision. Once a decision of the Board of Patent Appeals and Interferences is made, the losing party may appeal to the Court of Appeals for the Federal Circuit or file a civil action against the winning party in the appropriate United States district court.


An invention is conceived when a definite and permanent idea of an operative invention is known. Conception is complete when one of ordinary skill in the art could make the invention without undue research or experimentation.

During a patent interference, two important terms that may come up are "conception of the invention", and "reduction to practice". They sound simple, but in case law, not necessarily. 

One definition of conception of the invention is An invention is conceived when a definite idea of a particular invention is known. Conception is complete when one of ordinary skill in the art could make the invention without undue research or experimentation.  Good in theory, but as one can imagine, both sides in the interference will have different views of who had that "permanent idea" in their mind first. As mentioned above - evidence must be provided. This is why documented ideas in a notebook can be very important. 

Reduction to practice is the actual physical construction of an item, i.e. the invention, in physical form; something that can actually be shown to someone else doing what it is supposed to do.  

Examples, including but not limited to:

  • A machine: includes the actual building of the machine.  
  • An article or composition: includes the actual making of the article or composition.  
  • A process: includes the actual carrying out of the steps of the process. 

In either case, actual operation, demonstration, or testing for the intended use is usually necessary.  Of note, the filing of a regular application for patent completely disclosing the invention is treated as equivalent to reduction to practice.

As one can see, in practice, the situation can get quite complicated. Document everything!  Record all ideas on some form! The more one has to back a claim, the better the outcome.

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