Understanding the Doctrine of Equivalents in Patent Law

The Doctrine of Equivalents allows courts to hold an infringer liable even if their product does not literally infringe the patent claims.

What Is the Doctrine of Equivalents?

An accused product may still be considered infringing if it performs substantially the same function, in substantially the same way, to achieve the same result.

Key Principles

• Substantially the Same Function, Way, and Result
• Insubstantial Differences
• Prosecution History Estoppel
• No "Doubtful" Equivalents

Application in Patent Litigation

Used when a defendant argues their product doesn't literally infringe but performs the same function.