MPEP 2181: Means-Plus-Function Under 35 U.S.C. 112(f)

Answer in brief

MPEP 2181 uses a 3-prong test to decide whether a claim limitation invokes 35 U.S.C. 112(f). The limitation (A) uses "means", "step" or a generic placeholder, (B) modified by functional language, and (C) not modified by sufficient structure, material or acts to perform the function.

What MPEP 2181 covers

A 112(f) limitation is construed to cover the corresponding structure in the specification and its equivalents.

Generic placeholders, also called nonce terms, such as "module", "mechanism" or "unit", can invoke 112(f) without the word "means".
Functional language is often linked by "for", but also by "configured to" or "so that".
Using "means" creates a rebuttable presumption that 112(f) applies; omitting it creates a rebuttable presumption that it does not.
If the specification lacks corresponding structure, the claim is indefinite under 112(b).

How examiners use it

When a limitation invokes 112(f), the examiner states so in the Office action and identifies the corresponding structure, or rejects the claim if there is none.

On the patent bar

Know the 3-prong test and the presumptions tied to the word "means".

Read the full text

Official title: Identifying and Interpreting a 35 U.S.C. 112(f) or Pre-AIA 35 U.S.C. 112, Sixth Paragraph Limitation [R-07.2022].

Read MPEP 2181 in full on Wysebridge ↗

Or at the source: USPTO MPEP § 2181.

Questions & answers

What is the 3-prong test for 112(f)?

(A) the limitation uses "means", "step" or a generic placeholder; (B) it is modified by functional language; and (C) it is not modified by sufficient structure, material or acts to perform the function.

Sources for this entry

USPTO — MPEP § 2181 USPTO
Official text of this section, Ninth Edition, Revision 01.2024.
Wysebridge MPEP Center Wysebridge (publisher of this site)
The full MPEP (9th Ed., Rev. 01.2024) free to read, with Wysebridge's estimated patent bar weight for each chapter.

Practical guidance is original editorial content. Company-published figures are the company's own claims and are labeled as such.

Continue this reading path

MPEP 2173: Indefiniteness Under 35 U.S.C. 112(b)MPEP 2114: Functional Language in Apparatus Claims

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Cite or share this entry

MPEP.net. “MPEP 2181: Means-Plus-Function Under 35 U.S.C. 112(f).” Wysebridge Reference. Content reviewed 9 November 2026.
https://mpep.net/mpep-2181/