MPEP § 1875 — Unity of Invention Before the International Preliminary Examining Authority (Annotated Rules)

§1875 Unity of Invention Before the International Preliminary Examining Authority

USPTO MPEP version: BlueIron's Update: 2025-12-31

This page consolidates and annotates all enforceable requirements under MPEP § 1875, including statutory authority, regulatory rules, examiner guidance, and practice notes. It is provided as guidance, with links to the ground truth sources. This is information only, it is not legal advice.

Unity of Invention Before the International Preliminary Examining Authority

This section addresses Unity of Invention Before the International Preliminary Examining Authority. Primary authority: 37 CFR 1.475, 37 CFR 1.488, and 37 CFR 1.488(b)(2)). Contains: 7 requirements, 1 guidance statement, 4 permissions, and 1 other statement.

Key Rules

Topic

Article 19 Amendment Scope

7 rules
StatutoryRequiredAlways
[mpep-1875-b395e0bec9329e7800eb87cb]
Claim Restriction Required for Unity of Invention
Note:
Applicants must restrict claims or pay additional fees within the time limit if the International Preliminary Examining Authority finds lack of unity of invention.

(b) If the International Preliminary Examining Authority considers that the international application does not comply with the requirement of unity of invention, it may:

(3) If applicant fails to restrict the claims or pay additional fees within the time limit set for reply, the International Preliminary Examining Authority will issue a written opinion and/or establish an international preliminary examination report on the main invention and shall indicate the relevant facts in the said report.

Jump to MPEP Source · 37 CFR 1.488Article 19 Amendment ScopeArticle 19 Amendment TimingArticle 34 Amendments
StatutoryRequiredAlways
[mpep-1875-2003fd38d50fb53e0bc7e8e3]
Main Invention Is First Mentioned Claim
Note:
If unity of invention is disputed, the first claimed invention searched by the International Searching Authority is considered the main invention.

(b) If the International Preliminary Examining Authority considers that the international application does not comply with the requirement of unity of invention, it may:

In case of any doubt as to which invention is the main invention, the invention first mentioned in the claims and previously searched by an International Searching Authority shall be considered the main invention.

Jump to MPEP Source · 37 CFR 1.488Article 19 Amendment ScopeInternational Searching Authority (ISA)PCT Article 19 Amendments
StatutoryRecommendedAlways
[mpep-1875-ad907556de6d3519082effce]
Procedure for Lack of Unity Before International Preliminary Examining Authority
Note:
The process for addressing lack of unity of invention before the International Preliminary Examining Authority is governed by specific PCT and CFR rules, with initial reports often provided by the International Searching Authority.

The procedure before the International Preliminary Examining Authority regarding lack of unity of invention is governed by PCT Article 34(3)(a) through (c), PCT Rule 68 (see also PCT Rule 70.13), and 37 CFR 1.475 and 1.488. It should be noted that in most instances lack of unity of invention will have been noted and reported upon by the International Searching Authority which will have drawn up an international search report and a written opinion based on those parts of the international application relating to the invention, or unified linked group of inventions, first mentioned in the claims (“main invention”), unless the applicant has paid additional fees. If the applicant has paid additional search fees, additional inventions would also have been searched. No international preliminary examination will be conducted on inventions not previously searched by an International Searching Authority (37 CFR 1.488(b)(2)).

Jump to MPEP Source · 37 CFR 1.475Article 19 Amendment ScopeArticle 19 Amendment TimingArticle 34 Amendments
StatutoryPermittedAlways
[mpep-1875-ff443c26bb2c283833deb65b]
Examiner May Invite Claim Restriction to Comply with Unity of Invention Requirement
Note:
The examiner can request the applicant to restrict claims or pay additional fees if unity of invention is lacking, using specific forms.

If the examiner determines that unity of invention is lacking, there are two options:

(B) The examiner may invite the applicant to restrict the claims, so as to comply with the requirement, or pay additional fees, pointing out the categories of invention found using Form PCT/IPEA/405 or USPTO/499 (telephone practice). See MPEP § 1875.01.

Jump to MPEP Source · 37 CFR 1.488Article 19 Amendment ScopeInternational Preliminary Examining Authority (IPEA)Request Content and Form
StatutoryRequiredAlways
[mpep-1875-11af7033fe5ea3bbe770d0d2]
Claims Must Reflect Main Invention
Note:
If the applicant fails to respond to an invitation to restrict claims or pay additional examination fees due to lack of unity, the written opinion and international preliminary examination report must be based on the claims directed to what appears to be the main invention.

If the applicant fails to reply to the invitation to restrict the claims or pay additional examination fees due to lack of unity of invention (by not paying the additional fees or by not restricting the claims either sufficiently or at all), the written opinion, if any, and international preliminary examination report must be established on the claims directed to what appears to be the main invention (PCT Article 34(3)(c)). The main invention, in case of doubt, is the first claimed invention for which an international search report has been issued by the International Searching Authority. The main invention, as viewed by the examiner, must be set forth on Form PCT/IPEA/405.

Jump to MPEP Source · 37 CFR 1.488Article 19 Amendment ScopeArticle 34 AmendmentsWritten Opinion of ISA
StatutoryRequiredAlways
[mpep-1875-2b1d1f72a00acf34f86adb4f]
Examiner Examines Claimed Inventions After Fee Payment
Note:
If the applicant timely complies with an invitation to pay additional fees or restrict claims, the examiner will conduct international preliminary examination on those claimed inventions for which additional fees have been paid or to which the claims have been restricted.

If the applicant timely complies with the invitation to pay additional fees even under protest, or to restrict the claims, the examiner carries out international preliminary examination on those claimed inventions for which additional fees have been paid or to which the claims have been restricted. It should be noted that the national law of any elected State may provide that, where its national Office finds the invitation of the International Preliminary Examining Authority justified, those parts of the international application which do not relate to the main invention shall, as far as effects in that State are concerned, be considered withdrawn unless a special fee is paid by the applicant to that Office (PCT Article 34(3)(c)). Whether or not the question of unity of invention has been raised by the International Searching Authority, it may be considered by the examiner when serving as an authorized officer of the International Preliminary Examining Authority. In the examiner’s consideration, all documents cited by the International Searching Authority should be taken into account and any additional relevant documents considered. However, there are cases of lack of unity of invention, where, compared with the procedure of inviting the applicant to restrict the international application or pay additional fees (PCT Rule 68.2), little or no additional effort is involved in establishing the written opinion, if any, and the international preliminary examination report for the entire international application. Then reasons of economy may make it advisable for the examiner to use the option referred to in PCT Rule 68.1 by choosing not to invite the applicant to restrict the claims or to pay additional fees.

Jump to MPEP Source · 37 CFR 1.488Article 19 Amendment ScopeNationals and ResidentsReceiving Office (RO/US)
StatutoryPermittedAlways
[mpep-1875-d98b1c3bd146e8466fdb9a45]
Examiner May Skip Unity Check
Note:
The examiner can choose not to invite the applicant to restrict claims or pay additional fees if it is more economical, especially when there is no significant effort in establishing the written opinion for all inventions.

If the applicant timely complies with the invitation to pay additional fees even under protest, or to restrict the claims, the examiner carries out international preliminary examination on those claimed inventions for which additional fees have been paid or to which the claims have been restricted. It should be noted that the national law of any elected State may provide that, where its national Office finds the invitation of the International Preliminary Examining Authority justified, those parts of the international application which do not relate to the main invention shall, as far as effects in that State are concerned, be considered withdrawn unless a special fee is paid by the applicant to that Office (PCT Article 34(3)(c)). Whether or not the question of unity of invention has been raised by the International Searching Authority, it may be considered by the examiner when serving as an authorized officer of the International Preliminary Examining Authority. In the examiner’s consideration, all documents cited by the International Searching Authority should be taken into account and any additional relevant documents considered. However, there are cases of lack of unity of invention, where, compared with the procedure of inviting the applicant to restrict the international application or pay additional fees (PCT Rule 68.2), little or no additional effort is involved in establishing the written opinion, if any, and the international preliminary examination report for the entire international application. Then reasons of economy may make it advisable for the examiner to use the option referred to in PCT Rule 68.1 by choosing not to invite the applicant to restrict the claims or to pay additional fees.

Jump to MPEP Source · 37 CFR 1.488Article 19 Amendment ScopeInterviews in National StageExaminer Action on Protest
Topic

Article 34 Amendments

5 rules
StatutoryInformativeAlways
[mpep-1875-0283b4d31bf5703c80140a6b]
Requirement for Unity of Invention Before International Preliminary Examination
Note:
The International Preliminary Examining Authority must determine if the international application meets the unity of invention requirement before issuing any written opinion or report.

(a) Before establishing any written opinion or the international preliminary examination report, the International Preliminary Examining Authority will determine whether the international application complies with the requirement of unity of invention as set forth in § 1.475.

Jump to MPEP Source · 37 CFR 1.475Article 34 AmendmentsInternational Preliminary Examining Authority (IPEA)Unity of Invention Standard
StatutoryInformativeAlways
[mpep-1875-b80e7eae67e8bacf4cf9a3a8]
Requirement for Issuing Opinion on Lack of Unity
Note:
The International Preliminary Examining Authority must issue a written opinion indicating that unity of invention is lacking and specify the reasons without inviting further action or additional fees.

(b) If the International Preliminary Examining Authority considers that the international application does not comply with the requirement of unity of invention, it may (1) Issue a written opinion and/or an international preliminary examination report, in respect of the entire international application and indicate that unity of invention is lacking and specify the reasons therefor without extending an invitation to restrict or pay additional fees. No international preliminary examination will be conducted on inventions not previously searched by an International Searching Authority.

Jump to MPEP Source · 37 CFR 1.488Article 34 AmendmentsWritten Opinion of ISAUnity of Invention Standard
StatutoryInformativeAlways
[mpep-1875-1aaa3fe01e585b270e13edb7]
International Preliminary Exam Only After Previous Search
Note:
The International Preliminary Examining Authority can only conduct an examination if the invention has been previously searched by an International Searching Authority.

(b) If the International Preliminary Examining Authority considers that the international application does not comply with the requirement of unity of invention, it may (1) Issue a written opinion and/or an international preliminary examination report, in respect of the entire international application and indicate that unity of invention is lacking and specify the reasons therefor without extending an invitation to restrict or pay additional fees. No international preliminary examination will be conducted on inventions not previously searched by an International Searching Authority.

Jump to MPEP Source · 37 CFR 1.488Article 34 AmendmentsInternational Searching Authority (ISA)International Preliminary Examination (Chapter II)
StatutoryInformativeAlways
[mpep-1875-c3c2e9072b6872313484612b]
Inventions Not Previously Searched Cannot Be Examined
Note:
An international preliminary examination will not be conducted on inventions that were not previously searched by an International Searching Authority.

The procedure before the International Preliminary Examining Authority regarding lack of unity of invention is governed by PCT Article 34(3)(a) through (c), PCT Rule 68 (see also PCT Rule 70.13), and 37 CFR 1.475 and 1.488. It should be noted that in most instances lack of unity of invention will have been noted and reported upon by the International Searching Authority which will have drawn up an international search report and a written opinion based on those parts of the international application relating to the invention, or unified linked group of inventions, first mentioned in the claims (“main invention”), unless the applicant has paid additional fees. If the applicant has paid additional search fees, additional inventions would also have been searched. No international preliminary examination will be conducted on inventions not previously searched by an International Searching Authority (37 CFR 1.488(b)(2)).

Jump to MPEP Source · 37 CFR 1.475Article 34 AmendmentsInternational Searching Authority (ISA)International Preliminary Examination (Chapter II)
StatutoryRecommendedAlways
[mpep-1875-1be77321a52b0badb3b67b18]
All Cited Documents Must Be Reviewed for Lack of Unity
Note:
The examiner must review all documents cited by the International Searching Authority and any additional relevant documents, but may choose not to invite the applicant to restrict claims or pay fees if there is a lack of unity of invention.

If the applicant timely complies with the invitation to pay additional fees even under protest, or to restrict the claims, the examiner carries out international preliminary examination on those claimed inventions for which additional fees have been paid or to which the claims have been restricted. It should be noted that the national law of any elected State may provide that, where its national Office finds the invitation of the International Preliminary Examining Authority justified, those parts of the international application which do not relate to the main invention shall, as far as effects in that State are concerned, be considered withdrawn unless a special fee is paid by the applicant to that Office (PCT Article 34(3)(c)). Whether or not the question of unity of invention has been raised by the International Searching Authority, it may be considered by the examiner when serving as an authorized officer of the International Preliminary Examining Authority. In the examiner’s consideration, all documents cited by the International Searching Authority should be taken into account and any additional relevant documents considered. However, there are cases of lack of unity of invention, where, compared with the procedure of inviting the applicant to restrict the international application or pay additional fees (PCT Rule 68.2), little or no additional effort is involved in establishing the written opinion, if any, and the international preliminary examination report for the entire international application. Then reasons of economy may make it advisable for the examiner to use the option referred to in PCT Rule 68.1 by choosing not to invite the applicant to restrict the claims or to pay additional fees.

Jump to MPEP Source · 37 CFR 1.488Article 34 AmendmentsInternational Searching Authority (ISA)Written Opinion of ISA
Topic

International Preliminary Examining Authority (IPEA)

3 rules
StatutoryPermittedAlways
[mpep-1875-2cfaa554b94fe2b903f0073e]
IPEA May Issue Opinion on Lack of Unity
Note:
The International Preliminary Examining Authority may issue an opinion indicating that the international application lacks unity of invention and specify reasons without inviting restriction or additional fees.
(b) If the International Preliminary Examining Authority considers that the international application does not comply with the requirement of unity of invention, it may:
  • (1) Issue a written opinion and/or an international preliminary examination report, in respect of the entire international application and indicate that unity of invention is lacking and specify the reasons therefor without extending an invitation to restrict or pay additional fees. No international preliminary examination will be conducted on inventions not previously searched by an International Searching Authority.
  • (2) Invite the applicant to restrict the claims or pay additional fees, pointing out the categories of invention found, within a set time limit which will not be extended. No international preliminary examination will be conducted on inventions not previously searched by an International Searching Authority, or
  • (3) If applicant fails to restrict the claims or pay additional fees within the time limit set for reply, the International Preliminary Examining Authority will issue a written opinion and/or establish an international preliminary examination report on the main invention and shall indicate the relevant facts in the said report. In case of any doubt as to which invention is the main invention, the invention first mentioned in the claims and previously searched by an International Searching Authority shall be considered the main invention.
Jump to MPEP Source · 37 CFR 1.488International Preliminary Examining Authority (IPEA)Unity of Invention StandardPCT Unity of Invention
StatutoryRequiredAlways
[mpep-1875-6ae67c9b6289298bd103da04]
Main Invention Must Be Set on Form PCT/IPEA/405
Note:
The main invention, as determined by the examiner, must be specified on Form PCT/IPEA/405 in case of lack of unity of invention.

If the applicant fails to reply to the invitation to restrict the claims or pay additional examination fees due to lack of unity of invention (by not paying the additional fees or by not restricting the claims either sufficiently or at all), the written opinion, if any, and international preliminary examination report must be established on the claims directed to what appears to be the main invention (PCT Article 34(3)(c)). The main invention, in case of doubt, is the first claimed invention for which an international search report has been issued by the International Searching Authority. The main invention, as viewed by the examiner, must be set forth on Form PCT/IPEA/405.

Jump to MPEP Source · 37 CFR 1.488International Preliminary Examining Authority (IPEA)Interviews in National StageRequest Content and Form
StatutoryPermittedAlways
[mpep-1875-7bc4dfdc71b8c3bcfb05b6df]
Examiner May Consider Unity of Invention During IPEA
Note:
The examiner can evaluate the unity of invention when serving as an authorized officer for international preliminary examination, regardless of whether it was previously raised by the International Searching Authority.

If the applicant timely complies with the invitation to pay additional fees even under protest, or to restrict the claims, the examiner carries out international preliminary examination on those claimed inventions for which additional fees have been paid or to which the claims have been restricted. It should be noted that the national law of any elected State may provide that, where its national Office finds the invitation of the International Preliminary Examining Authority justified, those parts of the international application which do not relate to the main invention shall, as far as effects in that State are concerned, be considered withdrawn unless a special fee is paid by the applicant to that Office (PCT Article 34(3)(c)). Whether or not the question of unity of invention has been raised by the International Searching Authority, it may be considered by the examiner when serving as an authorized officer of the International Preliminary Examining Authority. In the examiner’s consideration, all documents cited by the International Searching Authority should be taken into account and any additional relevant documents considered. However, there are cases of lack of unity of invention, where, compared with the procedure of inviting the applicant to restrict the international application or pay additional fees (PCT Rule 68.2), little or no additional effort is involved in establishing the written opinion, if any, and the international preliminary examination report for the entire international application. Then reasons of economy may make it advisable for the examiner to use the option referred to in PCT Rule 68.1 by choosing not to invite the applicant to restrict the claims or to pay additional fees.

Jump to MPEP Source · 37 CFR 1.488International Preliminary Examining Authority (IPEA)International Searching Authority (ISA)Interviews in National Stage
Topic

Anticipation/Novelty

2 rules
StatutoryPermittedAlways
[mpep-1875-d668dcc52f71930f09deea83]
Invention Lacks Common Concept After Novelty Check
Note:
The International Preliminary Examining Authority may raise the objection that an invention lacks a common inventive concept if a document discovered during the search shows the claimed invention is not novel or obvious.

(c) Lack of unity of invention may be directly evident before considering the claims in relation to any prior art, or after taking the prior art into consideration, as where a document discovered during the search shows the invention claimed in a generic or linking claim lacks novelty or is clearly obvious, leaving two or more claims joined thereby without a common inventive concept. In such a case the International Preliminary Examining Authority may raise the objection of lack of unity of invention.

Jump to MPEP Source · 37 CFR 1.488Anticipation/NoveltyNovelty / Prior ArtObviousness
StatutoryPermittedAlways
[mpep-1875-b658091f4a8247f81635d598]
Objection for Lack of Unity of Invention
Note:
The International Preliminary Examining Authority may raise an objection if the invention claimed in a generic or linking claim lacks novelty or is obvious, leaving two or more claims without a common inventive concept.

(c) Lack of unity of invention may be directly evident before considering the claims in relation to any prior art, or after taking the prior art into consideration, as where a document discovered during the search shows the invention claimed in a generic or linking claim lacks novelty or is clearly obvious, leaving two or more claims joined thereby without a common inventive concept. In such a case the International Preliminary Examining Authority may raise the objection of lack of unity of invention.

Jump to MPEP Source · 37 CFR 1.488Anticipation/NoveltyNovelty / Prior ArtObviousness
Topic

International Searching Authority (ISA)

1 rules
StatutoryInformativeAlways
[mpep-1875-5e8b94370a587d644262a682]
Additional Inventions Searched If Fees Paid
Note:
If the applicant pays additional search fees, any additional inventions will also be searched during the international preliminary examination.

The procedure before the International Preliminary Examining Authority regarding lack of unity of invention is governed by PCT Article 34(3)(a) through (c), PCT Rule 68 (see also PCT Rule 70.13), and 37 CFR 1.475 and 1.488. It should be noted that in most instances lack of unity of invention will have been noted and reported upon by the International Searching Authority which will have drawn up an international search report and a written opinion based on those parts of the international application relating to the invention, or unified linked group of inventions, first mentioned in the claims (“main invention”), unless the applicant has paid additional fees. If the applicant has paid additional search fees, additional inventions would also have been searched. No international preliminary examination will be conducted on inventions not previously searched by an International Searching Authority (37 CFR 1.488(b)(2)).

Jump to MPEP Source · 37 CFR 1.475International Searching Authority (ISA)Search in National StageArticle 19 Amendment Scope
Topic

Interviews in National Stage

1 rules
StatutoryRequiredAlways
[mpep-1875-56e95c195a6d118e6d019496]
Examiner May Conduct International Preliminary Examination When Unity Lacks
Note:
If the examiner determines that unity of invention is lacking, they may conduct an international preliminary examination covering all claimed and previously searched inventions without inviting further restrictions or additional fees.
If the examiner determines that unity of invention is lacking, there are two options:
  • (A) The examiner may conduct an international preliminary examination covering all the claimed and previously searched inventions and indicate that unity of invention is lacking and specify the reasons therefor without extending an invitation to restrict or pay additional fees (PCT Rule 68.1), or
  • (B) The examiner may invite the applicant to restrict the claims, so as to comply with the requirement, or pay additional fees, pointing out the categories of invention found using Form PCT/IPEA/405 or USPTO/499 (telephone practice). See MPEP § 1875.01. The invitation to restrict or pay additional fees shall state the reasons for which the international application is considered as not complying with the requirement of unity of invention. (PCT Rule 68.2). Inventions not previously searched will not be considered or included in the invitation.
Jump to MPEP Source · 37 CFR 1.488Interviews in National StageUnity of Invention StandardPCT Unity of Invention
Topic

Unity of Invention Standard

1 rules
StatutoryRequiredAlways
[mpep-1875-426effcbeb6e3c1d8ff3e7fb]
Reasons for Unity Lack Must Be Stated
Note:
The examiner must provide reasons when inviting the applicant to restrict claims or pay additional fees due to lack of unity of invention.

If the examiner determines that unity of invention is lacking, there are two options:

The invitation to restrict or pay additional fees shall state the reasons for which the international application is considered as not complying with the requirement of unity of invention.

Jump to MPEP Source · 37 CFR 1.488Unity of Invention StandardPCT Unity of InventionPatent Cooperation Treaty
Topic

Patent Cooperation Treaty

1 rules
StatutoryRequiredAlways
[mpep-1875-7d8e1ff5fed09a79d6598461]
Unsearched Inventions Not Considered for Invitation
Note:
If the examiner determines that unity of invention is lacking, unsearched inventions will not be included in the invitation to restrict or pay additional fees.

If the examiner determines that unity of invention is lacking, there are two options:

(PCT Rule 68.2) Inventions not previously searched will not be considered or included in the invitation.

Jump to MPEP Source · 37 CFR 1.488Patent Cooperation TreatyInternational Preliminary Examining Authority (IPEA)Article 19 Amendment Scope
Topic

Article 19 Amendment Timing

1 rules
StatutoryInformativeAlways
[mpep-1875-2e4a71c21765d1914acd29be]
Main Invention Determined by First Search Report
Note:
The main invention is determined to be the first claimed invention for which an international search report has been issued, unless otherwise specified.

If the applicant fails to reply to the invitation to restrict the claims or pay additional examination fees due to lack of unity of invention (by not paying the additional fees or by not restricting the claims either sufficiently or at all), the written opinion, if any, and international preliminary examination report must be established on the claims directed to what appears to be the main invention (PCT Article 34(3)(c)). The main invention, in case of doubt, is the first claimed invention for which an international search report has been issued by the International Searching Authority. The main invention, as viewed by the examiner, must be set forth on Form PCT/IPEA/405.

Jump to MPEP Source · 37 CFR 1.488Article 19 Amendment TimingInternational Searching Authority (ISA)International Search Report

Citations

Primary topicCitation
Article 19 Amendment Scope
Article 34 Amendments
International Searching Authority (ISA)
37 CFR § 1.475
Article 19 Amendment Scope
Article 34 Amendments
International Searching Authority (ISA)
37 CFR § 1.488(b)(2)
Article 19 Amendment Scope
Interviews in National Stage
Patent Cooperation Treaty
Unity of Invention Standard
MPEP § 1875.01
Article 19 Amendment Scope
Article 19 Amendment Timing
Article 34 Amendments
International Preliminary Examining Authority (IPEA)
International Searching Authority (ISA)
PCT Article 34(3)(c)
Article 19 Amendment Scope
Article 34 Amendments
International Preliminary Examining Authority (IPEA)
International Searching Authority (ISA)
Interviews in National Stage
Patent Cooperation Treaty
Unity of Invention Standard
PCT Rule 68.1
Article 19 Amendment Scope
Article 34 Amendments
International Searching Authority (ISA)
PCT Rule 70.13

Source Text from USPTO’s MPEP

This is an exact copy of the MPEP from the USPTO. It is here for your reference to see the section in context.

BlueIron Last Updated: 2025-12-31