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Doctrine of Equivalents in Patent Prosecution: DOE Application, Festo Exceptions, Recent Case Law Developments

Recording of a 90-minute premium CLE video webinar with Q&A

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Conducted on Tuesday, December 13, 2022

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This CLE course will guide patent counsel on the doctrine of equivalents (DOE). The panel will discuss recent Federal Circuit DOE decisions applying the Festo exceptions, particularly the "tangential relation" exception. As the court held in Eli Lilly & Co. v. Hospira Inc. (Fed. Cir. 2019), "whether an amendment was merely tangential to an equivalent must be decided in the context of the invention disclosed in the patent and the prosecution history." Other recent Federal Circuit decisions on judicial exceptions to DOE will also be analyzed.


The DOE is a judicial doctrine that permits a court to find infringement when an accused product or process falls outside the literal language of the claims but is equivalent to and differs only insubstantially from the claimed invention. The concept of something infringing when the accused product "performs substantially the same function in substantially the same way to obtain the same result" can be found as far back as Sanitary Refrigerator Co. v. Winters, 280 U.S. 30, 42 (1929).

Prosecution history can operate as a limit on DOE. "The doctrine of prosecution history estoppel limits the doctrine of equivalents when the applicant makes a narrowing amendment for purposes of patentability, or clearly and unmistakably surrenders subject matter by arguments made to the examiner." Salazar v. Procter & Gamble Co. (Fed. Cir. 2005). The rationale for this principle is that the patentee should not be allowed to gain through the DOE claim scope that it gave up during prosecution to obtain allowance of the claims. The panel will discuss the example of argument-based prosecution history estoppel found in Amgen Inc. v. Coherus Biosciences Inc. (Fed. Cir. 2019).

According to the U.S. Supreme Court in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. (2002) (Festo VIII), a patentee can rebut the presumption that prosecution history estoppel applies if it shows that it comes within one of three exceptions. These exceptions are: the equivalent was unforeseeable at the time of the application, the rationale underlying the amendment bears no more than a tangential relation to the equivalent in question, or another reason suggesting that the patentee could not be expected to describe the insubstantial substitute.

Listen as our authoritative panel examines the lessons from recent Federal Circuit decisions for practitioners arguing for or against the Festo exceptions and, more broadly, for or against applying the DOE. The panel will also discuss hypothetical-claim analysis and ensnarement, disclosure-dedication, and all-limitations rule.



  1. Early DOE decisions; policy considerations
  2. Estoppel
    1. Argument-based
    2. Amendment-based
    3. Festo
      1. Exceptions
        1. The equivalent was unforeseeable at the time of the application
        2. Tangential relation
        3. An unreasonable expectation to describe the insubstantial substitute
  3. Hypothetical claims/ensnarement
  4. Disclosure-dedication
  5. All-limitations rule


The panel will review these and other important issues:

  • The reappearance of the Festo exceptions
  • The return of ensnarement
  • Best practices for drafting and prosecuting claims to minimize estoppel-preventing DOE arguments


Irving, Thomas
Thomas L. Irving

Finnegan Henderson Farabow Garrett & Dunner

Mr. Irving has 35 years of experience in the field of IP law. His practice includes due diligence, patent prosecution,...  |  Read More

McCurdy, Barbara
Barbara Clarke McCurdy

Finnegan Henderson Farabow Garrett & Dunner

Ms. McCurdy has more than 25 years of experience creating, enforcing, and defending patent rights, with a particular...  |  Read More

Murphy, Amanda
Dr. Amanda K. Murphy, Ph.D.

Finnegan Henderson Farabow Garrett & Dunner

Dr. Murphy focuses her practice on client counseling and patent prosecution for a range of clients. She prepares new...  |  Read More

O’Brien, Michelle
Michelle E. O'Brien

The Marbury Law Group

Ms. O’Brien has more than 20 years of experience representing domestic and foreign clients of all sizes in...  |  Read More

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