Inter Partes Review: How a Granted Patent Gets Challenged at the USPTO

A granted patent is not the end of the story. Any person or company can petition the USPTO's Patent Trial and Appeal Board to cancel claims in an issued patent through a proceeding called inter partes review, commonly abbreviated IPR. If you hold a patent, this is the main vehicle a competitor will use to attack it without going to court. If you are accused of infringement, IPR is often one of the first tools a defense attorney will reach for.

What Inter Partes Review Actually Is

IPR is an administrative trial conducted before the PTAB — a panel of administrative patent judges inside the USPTO. It was created by the America Invents Act and replaced an older procedure called inter partes reexamination. The proceeding is faster and more structured than district court litigation, and historically it has resulted in claim cancellation at a high rate, which is why it became popular almost immediately after it launched.

The only grounds allowed in an IPR are anticipation or obviousness based on prior art patents and printed publications. You cannot raise other invalidity arguments — like indefiniteness or improper inventorship — in an IPR. Those must go to court.

Who Can File and When

Anyone who is not the patent owner can file an IPR petition. The petition must be filed within one year of the date the petitioner was served with a complaint alleging infringement of that patent. Miss that window and you lose the right to petition, even if you have strong prior art in hand.

There is also an estoppel consequence worth understanding: once an IPR concludes, the petitioner generally cannot raise in later district court litigation any ground that was raised or reasonably could have been raised during the IPR. That is a significant strategic consideration before you file.

How the Proceeding Unfolds

The process runs in two phases.

Institution decision. After the patent owner has an opportunity to file a preliminary response, the PTAB decides whether to institute the IPR. The standard is whether there is a reasonable likelihood that the petitioner would prevail on at least one challenged claim. If the board does not institute, the proceeding ends there.

Trial phase. If the board institutes, the case proceeds to a full trial on the merits. The patent owner can file a response, submit expert declarations, and — within limits — amend claims. The petitioner can reply. There is typically a hearing before the panel. The board then issues a final written decision.

What Can Happen to the Claims

• Claims can be canceled outright if the board finds them unpatentable.
• Claims can survive if the board finds the prior art does not anticipate or render them obvious.
• The patent owner can propose substitute claims through a motion to amend, though the PTAB applies its own standards for what amendments are permissible and the process is difficult.

A canceled claim is gone permanently. There is no reissue path that brings back a claim the PTAB has canceled on the merits.

Why Patent Holders and Accused Infringers Both Need to Understand This

If you own a patent and are considering asserting it, expect that any well-resourced defendant will search for prior art and evaluate whether an IPR petition is viable. A patent that looks strong on its face can have vulnerabilities that only surface under PTAB scrutiny. That reality affects licensing negotiations, litigation budgets, and how aggressively you pursue a demand.

If you are on the receiving end of an assertion, IPR is not automatically the right move. Filing a petition starts the one-year estoppel clock, costs money, and — if you lose at institution or on the merits — can leave you in a worse position in parallel litigation. The decision requires weighing the strength of the prior art, the timing of litigation, and the estoppel consequences.

The Parallel Litigation Problem

District court litigation and IPR often run simultaneously. Courts have discretion to stay district court proceedings pending an IPR, but they do not always do so. Managing two parallel proceedings — with different timelines, different standards of proof, and different procedural rules — is one of the more complex situations in patent practice.

Practical Takeaways

• IPR lets anyone challenge issued patent claims at the PTAB using prior art patents and printed publications — no lawsuit required to initiate it.
• The one-year deadline from service of an infringement complaint is a hard cutoff; missing it eliminates the IPR option for an accused infringer.
• A petitioner who goes through IPR is generally estopped from raising the same grounds — or grounds that reasonably could have been raised — in later district court litigation.
• Canceled claims are permanently gone; surviving an IPR can actually strengthen a patent's credibility in licensing and litigation.
• Patent owners should evaluate IPR vulnerability before asserting a patent, not after a petition lands.
• The decision to file an IPR petition involves strategic tradeoffs that go well beyond simply having strong prior art in hand.

This guide is general education, not legal advice, and does not create an attorney–client relationship. For your specific situation, talk to a registered patent attorney.