A Blog About Intellectual Property Litigation and the District of Delaware


Entries for tag: Reverse DOE

Fish Traps
Chris J Walker, Unsplash

We first posted a reminder that reverse DOE and ensnarement exist back in 2021, and then again in 2023. But here, now, in 2025, we just got some nice guidance from the Court about ensnarement, and it seems like a great time to put out another reminder.

What Are They?

The Reverse Doctrine of Equivalents deals with a situation where the accused product literally reads on the claims, but is not actually doing what the patent is meant to cover. As we noted last time:

The [reverse doctrine of equivalents] rescues from infringement devices that literally satisfy the elements of a claim but perform the same function of the invention in a …

"Yes, your honor, it literally meets the claim elements of an 'animal' in a 'structure' with a 'gable roof.' But under the reverse doctrine of equivalents . . ." Go to Tomas Tuma's profile Tomas Tuma, Unsplash

The reverse doctrine of equivalents and ensnarement are great for accused infringers, but for whatever reason they often seem to get set by the wayside.

RDOE for You and Me

Reverse doctrine of equivalents has a terrible name. It's really just the argument that even if the accused product meets the literal elements of the claim, it does not infringe because it is performs the claimed function in a substantially different way than the claimed invention.

As Judge Connolly put it …

Coffee Equals
Charles "Duck" Unitas, Unsplash

Most patent litigators know that the reverse doctrine of equivalents exists, and provides a way to argue non-infringement even if an accused product meets the literal terms of a claim. But it tends to be one of those issues that floats around in the ether, waiting for the right case, and it is rarely applied in practice.

Judge Connolly had an occasion last week to address the issue, resolving a motion for summary judgment of no reverse DOE, and took the opportunity to dig into some of the history of the reverse doctrine of equivalents. He first quoted the Federal Circuit's description of what the doctrine is:

the reverse doctrine of equivalents . . …