35 U.S.C. · Part II · Chapter 11, Application for patent
35 U.S.C. 121: Divisional applications
In plain English
If one application claims two or more independent and distinct inventions, the USPTO may require the applicant to restrict the application to one of them. The applicant elects one invention, the other claims are withdrawn, and the withdrawn inventions can be pursued in divisional applications that keep the original filing date if they meet section 120.
Section 121 gives divisionals a safe harbor. A patent issued on the restricted application, or on an application filed as a result of the restriction, cannot be used as a reference against the divisional, the original application or patents issued on either, provided the divisional is filed before the other patent issues. In practice that protects divisionals from obviousness-type double patenting rejections over their siblings.
The last sentence is a protection for patentees: the validity of a patent cannot be questioned because the USPTO failed to require restriction.
Annotation by Raj Sutariya, Co-founder, PatentAssist.ai. General information, not legal advice; the statute below governs.
Text of 35 U.S.C. 121
Current text, quoted from the official United States Code.
If two or more independent and distinct inventions are claimed in one application, the Director may require the application to be restricted to one of the inventions. If the other invention is made the subject of a divisional application which complies with the requirements of section 120 it shall be entitled to the benefit of the filing date of the original application. A patent issuing on an application with respect to which a requirement for restriction under this section has been made, or on an application filed as a result of such a requirement, shall not be used as a reference either in the Patent and Trademark Office or in the courts against a divisional application or against the original application or any patent issued on either of them, if the divisional application is filed before the issuance of the patent on the other application. The validity of a patent shall not be questioned for failure of the Director to require the application to be restricted to one invention.
Practical notes
A restriction requirement with no action on the merits normally sets a 2-month reply period (MPEP 710). You must elect even if you disagree. To keep the right to petition, traverse in the reply and give reasons (37 CFR 1.143 and 1.144); an election without traverse cannot be challenged later.
The safe harbor is narrower than it looks. It does not apply to applications filed voluntarily without a restriction requirement, to continuation-in-part applications that include the restricted claims, or to claims that drift across the line the examiner drew. The claims of the divisional must stay consonant with the restriction (MPEP 804.01).
Restriction can be useful. A divisional family lets you pursue each invention with its own claims and timeline. Budget for it: each divisional pays its own filing, search, examination and issue fees and, once granted, its own maintenance fees.
Related rules and guidance
- 37 CFR
- § 1.141, § 1.142, § 1.143, § 1.144, § 1.146
- MPEP
- 802, 803, 804, 806, 817, 821
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All annotated sections of 35 U.S.C.
Statute text from the United States Code published by the Office of the Law Revision Counsel of the U.S. House of Representatives (uscode.house.gov). Text contains those laws in effect through Public Law 119-124 (October 15, 2026). Editorial notes and footnotes are omitted. The annotations are general information, not legal advice; check the official text and a registered patent practitioner before relying on them.