What is a Jepson claim?

A Jepson claim is a patent claim format for improvement inventions. It separates the known prior-art context from the applicant's actual improvement, using a preamble to describe everything already in the art and then introducing the novel contribution after a transitional phrase. The format is defined in 37 CFR 1.75(e), which specifies that an improvement claim should contain: a preamble comprising a general description of all the elements or steps of the claimed combination which are conventional or known; a phrase such as "wherein the improvement comprises"; and those elements, steps, or relationships that constitute the new or improved portion.

The format is named after Ex parte Jepson, an administrative decision from 1917, and was formally codified in USPTO rules in 1967.

Structure

A Jepson claim for an improvement to a bicycle brake might read:

"In a bicycle braking system comprising a brake lever, a cable connecting the lever to a brake caliper, and a brake pad contacting the rim, wherein the improvement comprises a temperature-sensitive polymer layer bonded to the brake pad surface."

The preamble recites the conventional assembly. Everything after "wherein the improvement comprises" is what the applicant claims as new. The format makes the boundary between old and new explicit on the face of the claim.

The prior art admission trap

The structural clarity of a Jepson claim comes with a significant cost. Drafting a claim in Jepson format is taken as an implied admission that the subject matter of the preamble is the prior art work of another. An examiner or court may treat the preamble as admitted prior art without needing a separate documentary reference confirming what the preamble says.

In In re Fout, 675 F.2d 297 (CCPA 1982), the court held that the preamble of a Jepson-type claim constitutes admitted prior art where the applicant's specification credited another as the inventor of the preamble subject matter. The practical consequence is direct: by choosing Jepson format, the applicant has effectively conceded the preamble to the public domain for purposes of novelty and obviousness analysis. The examiner does not need to cite a documentary reference for what the preamble states; the applicant's own claim format is the reference.

Two exceptions to the implied admission

The implied admission is rebuttable in two recognized circumstances.

Exception 1: Preamble describes the applicant's own work. Where the preamble of a Jepson claim describes the applicant's own prior work rather than the work of another, the preamble may not be used against the claims as prior art, as established in Reading & Bates Construction Co. v. Baker Energy Resources Corp., 748 F.2d 645 (Fed. Cir. 1984). To invoke this exception, the applicant should affirmatively state on the prosecution record that the preamble elements are their own earlier work, not the work of a third party. Leaving it to inference risks waiving the protection.

Exception 2: Another credible reason for the format. The implied prior art admission may also be overcome if the applicant provides another credible reason for using Jepson format, such as to avoid a double patenting rejection in a co-pending application, as recognized in In re Ehrreich, 590 F.2d 902 (CCPA 1979). This exception requires an affirmative explanation in the prosecution history. A bare choice of Jepson format, without an accompanying explanation, will not invoke it.

The written description requirement: In re Xencor (2025)

A longstanding question in Jepson claim practice was whether a preamble, having been labeled "prior art," still needed written description support in the specification. The Federal Circuit settled that question in In re Xencor, Inc., Appeal No. 24-1870 (Fed. Cir. Mar. 13, 2025): the limiting preamble of a Jepson claim must be supported by adequate written description under 35 U.S.C. § 112(a), and applicants cannot rely on the Jepson format to avoid written description for preamble elements they characterize as conventional.

In Xencor, the applicant's Jepson claim recited a method of treating a patient by administering an anti-C5 antibody, and the applicant argued the preamble required no written description because it recited well-known prior art; the Federal Circuit affirmed the Patent Trial and Appeal Board's written description rejection.

The standard the court established: adequate written description for a Jepson claim requires the applicant to establish that what is claimed to be well known in the prior art is, in fact, well known in the prior art. It is not enough to label preamble language as "conventional" or "well known." The applicant must either describe the conventional baseline in the specification or be able to demonstrate through record evidence that it is genuinely established in the field.

Why Jepson claims are rarely used today

The prior art admission and the Xencor written description requirement together make Jepson claims a difficult format to use safely. Jepson claims have declined dramatically in US patent practice, from over 8% of patents in the early 1980s to less than 0.1% in recent years. Most US practitioners instead draft conventional independent claims, where the preamble does not automatically generate an implied prior art admission and where the written description burden is no different from the rest of the claim.

Jepson vs. conventional independent claims: when the format still makes sense

Jepson format can still be appropriate in narrow circumstances:

• When a crowded art field makes the improvement boundary genuinely important to distinguish on the face of the claim, and the applicant is confident the prior art context in the preamble is solid and cannot be weaponized against the improvement body.
• When the applicant's own prior work forms the preamble and the "own prior work" exception clearly applies, removing the implied admission risk.
• When counsel has chosen Jepson format to address a double patenting concern and has recorded that reason in the prosecution history.

Outside these circumstances, a conventional independent claim phrased to make the improvement clear is the safer choice.

Practical notes

• Avoid Jepson format by default. A conventional independent claim can highlight the same improvement without triggering the automatic prior art admission. The clarity benefit rarely outweighs the admission risk.
• If the preamble describes your own prior work, state that explicitly on the record. The Reading & Bates exception protects you only if the prosecution history makes clear that the preamble elements originate with the applicant, not a third party.
• If you use Jepson to avoid double patenting, explain it. The In re Ehrreich safe harbor requires an affirmative statement of the reason on the prosecution record. A silent choice of Jepson format does not invoke it.
• After Xencor, ensure the specification supports the preamble. Before filing, verify that the specification describes the conventional elements in the preamble or that you have evidence they are genuinely well known. Merely calling them "well known" without support is no longer a safe approach.
• If you convert a non-Jepson application to Jepson format during prosecution, consider whether new matter issues arise. Shifting the prior art boundary via claim amendment can create written description complications on top of the admission risk.