Unity of Invention Under Different Jurisdictions: India, PCT, EPC and US

Unity of invention decides how many inventions one patent application may claim. India, the PCT and the EPC ask whether the claims form one inventive concept, but only the PCT and the EPC define it through special technical features. The United States applies restriction (independent or distinct inventions) to ordinary filings and unity only to national stage applications.

This comparison is written for in-house and foreign counsel managing a patent family that runs through the Indian Patent Office, the European Patent Office, the US Patent and Trademark Office and the PCT. It rests on the PCT Regulations as published by WIPO in October 2026 (in force from 1 January 2026), the PCT International Search and Preliminary Examination Guidelines, the EPC 17th edition with amendments to December 2023 and the EPO Guidelines for Examination, the MPEP Revision 01.2024, the Patents Act text to 1 August 2024 and the 2024 Amendment Rules (verified as of October 2026). It flags where a point rests on office practice rather than on a statute or rule.

Quick answer: The PCT and the EPC test whether the claims share the same or corresponding special technical features. India tests for a single inventive concept under section 10(5) of the Patents Act, 1970. The United States may require restriction of independent and distinct inventions, with MPEP practice asking whether examining them together would be a serious burden, but it tests national stage entries by unity, so a 111(a) application claiming benefit of a PCT application is still subject to restriction practice. Responses differ: pay additional fees within one month (PCT) or two months (EPO); contest, amend or divide before grant in India; elect, and divide where needed, in the United States.

How unity of invention is tested in each system

The PCT, the EPC and India each ask whether claimed inventions form one inventive concept, but only the PCT and the EPC define the test through special technical features. The United States separates two tests: restriction for ordinary applications and unity for national stage applications. The table sets out the test, the governing text and the usual response.

The wording of the first three rows is closely related. PCT Rule 13.2 and EPC Rule 44(1) both define special technical features by reference to a contribution that each claimed invention, considered as a whole, makes over the prior art. Section 10(5) of the Patents Act speaks of a single inventive concept and does not itself use the expression special technical features.

The fourth and fifth rows show why a family-wide view matters: the filing route, not the invention, sets the US test. An application under 111(a), including one that claims benefit of a PCT application, is subject to restriction practice, while the same invention entering through the national stage is tested for unity (MPEP 1893.03(d)). The sections below take each system in turn, using national phase and national stage for the same step of entering a country from the PCT, as each system does.

The PCT test and the additional fee procedure

Under PCT Rule 13, unity exists only where inventions share a technical relationship through the same or corresponding special technical features, meaning features that define a contribution over the prior art. If the International Searching Authority finds no unity, it invites additional search fees payable within one month, and the applicant may pay under protest.

Rule 13.1 sets the requirement for unity of invention under the PCT: the international application must relate to one invention only or to a group of inventions so linked as to form a single general inventive concept. Rule 13.2 then makes unity depend on a technical relationship involving “one or more of the same or corresponding special technical features”. Because the definition measures contribution over the prior art, a feature common to all claims supplies unity only if it is itself a contribution over that art. The PCT International Search and Preliminary Examination Guidelines (paragraph 10.03) describe this as the difference between lack of unity a priori, evident before any prior art is considered, and a posteriori, apparent only after the prior art is taken into account. Their example: claims to A + X and A + Y have unity a priori through A, but if A turns out to be known or obvious there may be lack of unity a posteriori, because A no longer defines a contribution over the prior art. A citation against the common feature does not settle the point by itself: paragraph 10.04 says lack of unity should neither be raised nor persisted in on a narrow, literal or academic approach, and paragraph 10.08 directs the examiner to consider whether the dependent claims still share an inventive link.

Rule 13.3 removes the manner of claiming from the analysis: the determination is made without regard to whether inventions appear in separate claims or as alternatives within a single claim. Rule 13.4 allows a reasonable number of dependent claims claiming specific forms of an independent claim, even where a dependent claim’s features could be considered an invention in themselves, subject to Rule 13.1.

Rule 40.1 governs the invitation. It must give the reasons for the finding, invite payment of the additional fees within one month from the date of the invitation, and, where applicable, invite payment of a protest fee within the same month. Under Rule 40.2(c) the applicant may pay under protest with a reasoned statement that the application complies with unity or that the fee is excessive. A review body within the Authority examines the protest and orders total or partial reimbursement to the extent it finds the protest justified.

Two details matter for later planning. On the applicant’s request, the text of the protest and the decision is notified to the designated Offices with the international search report. If the protest fee required under Rule 40.1(iii) is not paid within the time limit, Rule 40.2(e) treats the protest as not made, and that protest fee is refunded where the review body finds the protest entirely justified.

Where the search is made on the main invention only or on less than all the inventions (Article 17(3)(a)), the search report indicates which parts of the application were and were not searched (Rule 43.7), and 37 CFR 1.476(c) states that the USPTO as Authority searches the invention first mentioned where no additional fees are paid. At the preliminary examination stage, Rule 68.2 allows the International Preliminary Examining Authority to invite the applicant, at the applicant’s option, to restrict the claims or to pay additional fees, within one month from the date of the invitation. In case of doubt, Rule 68.5 treats the invention first mentioned in the claims as the main invention.

The EPC test and the further search fee

Article 82 EPC requires one invention or a group linked by a single general inventive concept, and Rule 44 closely tracks the PCT wording on special technical features. Where unity is lacking, the EPO searches the first-mentioned invention and invites a further search fee for each other invention, payable within two months.

Rule 44(1) provides that unity “shall be fulfilled only when there is a technical relationship” among the inventions involving the same or corresponding special technical features. Rule 44(2) repeats the rule that the manner of claiming, whether in separate claims or as alternatives within one claim, does not change the determination.

Rule 64(1) sets the consequence. The EPO draws up a partial search report on the parts of the application relating to the invention, or group of inventions, first mentioned in the claims, and informs the applicant that a further search fee must be paid for each invention involved within two months. The search report is then drawn up for the parts relating to inventions for which search fees have been paid. Rule 64(2) provides for refund of a fee paid under paragraph 1 if the applicant requests it during examination and the Examining Division finds the communication was not justified.

Rule 164 applies the same mechanism to supplementary European searches. Under Rule 164(2), where the supplementary search is dispensed with and the Examining Division considers that the claims cover an invention not searched by the EPO as International Searching Authority or as authority specified for supplementary international search, it informs the applicant that a search will be performed for any such invention for which a search fee is paid within two months. Rule 164(1) applies the same two-month further fee mechanism where the EPO draws up a partial supplementary search report. The 17th edition of the EPC text cross-refers Rule 64 as a whole to the Enlarged Board of Appeal opinion G 2/92, titled “Non-payment of further search fees”, and Rule 64(2) to decision G 1/11. Counsel advising on unpaid fees should read both; this article states G 2/92 only as the Guidelines apply it.

Non-payment has a lasting effect, and the governing provisions are Rule 64 and G 2/92, or Rule 164 for Euro-PCT applications, not Rule 137(5). The EPO Guidelines for Examination (H-II 6.2) state that where a further search fee was not paid for an originally claimed invention and the lack of unity objection is maintained, the applicant must restrict the claims to a searched invention in line with G 2/92; an application restricted to an unsearched originally claimed invention can be refused under Rule 64, and in a Euro-PCT case the Examining Division objects under Rule 164(2)(c), or Rule 164(1) where the EPO carried out a supplementary search, and can refuse under Rule 164 if the applicant does not limit the claims to a searched invention. The Guidelines add that Rule 137(5) cannot be invoked where the search fee for an originally claimed invention was not paid; Rule 137(5) itself bars amended claims to unsearched subject-matter that does not combine with the originally claimed invention into a single general inventive concept. The unsearched invention can be pursued in a divisional application, which Rule 36(1) allows relating to any pending earlier European patent application, deemed filed on the earlier filing date under Article 76(1) to the extent it does not extend beyond the earlier application as filed.

The Indian position under sections 7, 10 and 16

Indian law states the requirement twice. Section 7(1) says every application shall be for one invention only, and section 10(5) says the claims shall relate to a single invention or to a group linked so as to form a single inventive concept. The remedy is a further application under section 16, filed before grant.

Section 16(1) is the working provision for unity of invention in India. It lets an applicant file a further application, at any time before the grant of the patent, either if the applicant so desires or to remedy the Controller’s objection that the claims relate to more than one invention. Under section 16(2) the further application must carry its own complete specification and may not include matter not in substance disclosed in the complete specification of the first application. Section 16(3) lets the Controller require amendment so that neither specification claims matter claimed in the other.

The Explanation to section 16 deems the further application to have been filed on the date of the first application, and it proceeds as a substantive application examined when a request for examination is filed within the prescribed period. Rule 13(2A), inserted by G.S.R. 211(E) of 15 March 2024, lets an applicant file one or more further applications under section 16, including in respect of an invention disclosed in the provisional or complete specification or a further application filed under section 16. An appeal lies to the High Court from a Controller’s order under section 15 or section 16 (section 117A(2)), within three months under section 117A(4).

Rule 13(2A) operates under section 16, and the words “if he so desires” still require a plurality of inventions in the specification. The Division Bench of the Delhi High Court in Syngenta Limited v Controller of Patents and Designs (C.A.(COMM.IPD-PAT) 471/2022, 13 October 2023) held that a further application under section 16 is maintainable provided the plurality of inventions is disclosed in the provisional or complete specification, whether filed on the applicant’s own motion or to meet a Controller’s objection, and overruled the contrary reading in Boehringer Ingelheim that required the plurality to appear in the parent claims (paragraphs 21, 25 and 32). The further application must still claim a different invention disclosed in the first specification and satisfy section 16(2) and (3).

Responding to the objection and filing the further application run on different clocks. Section 21(1) deems an application abandoned unless the applicant complies, within the prescribed period, with all requirements imposed on the applicant, counted from the first statement of objections. The Manual states that period as six months from issuance of the first examination report, extendable once by up to three months on a request in Form 4 (Rule 24B(5) and (6); the 2024 Amendment Rules changed the wording of the request cut-off in sub-rule (6), so check the current text before relying on the Manual’s timing). Section 16(1) measures the window to grant, but section 21(1) can end the application earlier by deemed abandonment, so on these texts the further application is in practice planned against the examination clock rather than against grant. The Manual (06.01.03) states that a divisional is treated as a substantive application, so separate fees are payable and a separate request for examination must be made.

An international application designating India has effect as an application under section 7, 54 or 135, as the case may be, with its title, description, claims, abstract and drawings taken as the complete specification (section 138(4)), so on that reading section 10(5) applies on national phase entry. For the national phase mechanics and the treatment of an International Searching Authority objection, see unity of invention for PCT national phase applications in India.

Lack of unity matters at examination but not afterwards. Section 46(2) provides that a patent shall be granted for one invention only, with a proviso that no person may take objection in a suit or other proceeding that a patent was granted for more than one invention. Lack of unity does not appear among the listed grounds of opposition in section 25 or of revocation in section 64(1).

The Manual of Patent Office Practice and Procedure, version 3.0 (2019), paragraph 09.03.08, describes Patent Office practice rather than statute. It states that unity is determined without regard to whether inventions are claimed in separate claims or as alternatives, and gives as examples of a single inventive concept a product with a process specially adapted to make it, and a process with an apparatus specifically designed to carry it out. For the mechanics of dividing an application, see divisional patent applications in India.

The United States, restriction for ordinary filings and unity for national stage

A US application filed under 35 U.S.C. 111(a) is tested by restriction: the Director may require restriction where two or more independent and distinct inventions are claimed. A national stage application entering under section 371 is tested for unity under 37 CFR 1.475 instead, the same standard the PCT applies.

Section 121 provides that if two or more independent and distinct inventions are claimed in one application, the Director may require restriction to one of them. Under 37 CFR 1.141(a) such inventions may not be claimed in one national application, except that a reasonable number of species may be claimed where an allowable generic claim exists. Under 37 CFR 1.142(a) the examiner will require the applicant to elect an invention, normally before any action on the merits but at any time before final action.

Two points come from the MPEP, which records examining practice rather than the rule text. MPEP 803 states that claims may be restricted only if they are able to support separate patents and are either independent or distinct, and that if search and examination of all claims can be made without serious burden, the examiner must examine them on the merits even though they include independent or distinct inventions. MPEP 802.02 defines restriction as the practice of requiring an applicant to elect a single claimed invention where independent or distinct inventions are claimed.

National stage applications follow a different rule. Rule 1.475(a) adopts the PCT definition of unity, merging PCT Rules 13.1 and 13.2 for international and national stage applications, with the special technical features sentence in the same words, and Rule 1.475(b) lists category combinations considered to have unity, such as a product and a process specially adapted for its manufacture. Under 37 CFR 1.499 an examiner who finds a lack of unity under 1.475 may require an election, before any action on the merits or at any time before the final action at the examiner’s discretion. MPEP 1893.03(d) describes the unity analysis at the national stage as “(not an independent and distinct analysis)” and states that restriction practice under 37 CFR 1.141 to 1.146 continues to apply to applications filed under 111(a), even where the application claims benefit of an earlier international application designating the United States.

Where the tests diverge on the same claims

The same claim set can pass one system and draw an objection in another. A product claim with a process claim specially adapted to make it has unity under 37 CFR 1.475(b), and the Indian Manual gives the same pairing. In a US 111(a) filing the examiner can still require restriction if the MPEP distinctness conditions are shown.

Take a hypothetical claim set: claim 1 covers a battery electrode material, claim 12 a process of making that material, and claim 18 a method of using the material in a cell. At the national stage, 37 CFR 1.475(b)(3) treats a product, a process specially adapted for its manufacture and a use of the product as having unity if the claims are drawn only to that combination. In India, the Manual’s examples include a product with a process specially adapted for its manufacture, and a mould, a method of making it and a process of casting using it as a single invention, which point the same way as a matter of practice, though no example deals with a battery material use claim as such. Neither result is guaranteed, because the examiner or Controller still reads the actual claims.

In a US 111(a) filing the analysis changes. MPEP 806.05(f) states that a process of making and a product made by it can be shown to be distinct if the process is not an obvious process of making the product and can make another materially different product, or if the product can be made by another materially different process. If the applicant convincingly traverses, the burden shifts to the examiner to document a viable alternative process or product, or withdraw the requirement. Under 37 CFR 1.141(b), a three-way requirement among product, process of making and process of use can be made only where the process of making is distinct from the product.

The PCT and the EPC reach the same combination through their guidelines rather than their rules. The PCT International Search and Preliminary Examination Guidelines, paragraph 10.12(i), read Rule 13 as permitting, with an independent product claim, an independent claim for a process specially adapted for the manufacture of that product and an independent claim for a use of the product; paragraph 10.13 treats a process as specially adapted where it inherently results in the product, and paragraph 10.16 requires a single general inventive concept to link the categories, with the essence of the invention residing primarily in the product. The EPO Guidelines (F-V 3) say the same in different words: common matter may be found in claims of different categories, so a product may be the common matter present in a process specially adapted for its manufacture and in a use of that product, and unity then turns on whether that common matter is a contribution over the prior art. On both texts claims 1, 12 and 18 can stand together if the electrode material itself is the contribution.

A second divergence concerns alternatives. PCT Rule 13.3, EPC Rule 44(2) and the Indian Manual each say the manner of claiming does not change the unity determination, so packing different inventions into one claim as alternatives does not avoid the test. The US species rules work differently: 37 CFR 1.141(a) permits a reasonable number of species with an allowable generic claim, and 37 CFR 1.146 lets the examiner, in the first action on an application with a generic claim and claims to more than one patentably distinct species, require election of a species if no claim to the genus is found allowable.

Responding to an objection or restriction requirement

Each system offers a different choice: pay for further searches at the PCT and the EPO, elect and divide in the United States, or contest, amend or divide in India. The right choice depends on whether the unsearched or non-elected inventions still matter commercially, because each route costs a fee now or a separate application later.

A practical decision rule follows from these texts, and it is advice rather than a requirement. Where a further invention is commercially important in the jurisdiction concerned, preserve it before the window closes: pay the fee or file the divisional. Where it is not, accept the narrower search or election and record the decision; at the EPO an unsearched originally claimed invention is then pursued, if at all, in a divisional application filed while the earlier application is pending. A protest at the PCT stage is worth considering where unity is arguable, because Rule 40.2(c) provides for reimbursement to the extent the protest is justified, and a protest fee may be required under Rule 40.2(e), refundable where the review body finds the protest entirely justified.

In the United States, reconsideration under 37 CFR 1.143 must include a provisional election of one invention. After a final requirement the applicant may petition under 1.144, which may be deferred until after final action or allowance of the elected claims but must be filed not later than appeal, and a petition is not considered if reconsideration was not requested. Under section 121, a patent issuing on an application subject to a restriction requirement shall not be used as a reference against a divisional application, or against the original, if the divisional is filed before the patent issues on the other application. Entitlement to the earlier filing date and protection under section 121 are separate questions. A divisional that complies with section 120 is entitled to the benefit of the original filing date, and 37 CFR 1.78 frames such benefit claims by reference to a prior-filed copending application. The section 121 bar is conditional: MPEP 804.01 states, in the context of nonstatutory double patenting rejections, that it applies only where the Office has made a restriction requirement, that it does not apply to a divisional filed voluntarily, and that the claims must remain consonant with the restriction requirement, meaning the line of demarcation between the inventions identified by the examiner must be maintained.

A divisional does not answer the parent’s restriction requirement; the reply to the parent must still elect, with or without traverse (37 CFR 1.143). MPEP 810 sets a 2-month shortened statutory period for reply when a written restriction requirement is made without an action on the merits, extendable under 37 CFR 1.136(a). Election does not necessarily mean a divisional: MPEP 806.05(f) states that withdrawn process claims that include all the limitations of an allowable product claim should be considered for rejoinder (see MPEP 821.04).

The national and regional offices also keep their own power to find a lack of unity. MPEP 1893.03(d) states that the US examiner may make a lack of unity requirement in a national stage application even if no such requirement was made by the ISA or IPEA, and EPC Rule 164(2) provides for the Examining Division to inform the applicant that a search will be performed for an invention not searched by the EPO as ISA if a search fee is paid within two months. The Indian Manual (07.02.07) states generally that ISA and IPEA opinions are non-binding on member countries, without addressing unity findings in terms. An international finding therefore does not settle the question in the United States or at the EPO, and India applies its own section 10(5).

For how that plays out in Indian national phase practice, see the page on PCT patent applications in India. For divisional practice in China, which this article does not cover, see divisional patents in various jurisdictions.

Drafting for unity before the first filing

Build the claim set around one feature that defines a contribution over the prior art, then tie each other independent claim to it. Dependent claims are permitted in reasonable numbers under PCT Rule 13.4, and packing different inventions into one claim as alternatives does not change the unity assessment under Rule 13.3.

The specification matters as much as the claims. An Indian further application under section 16(2) may not include matter not in substance disclosed in the first application’s complete specification, so each invention that may later be divided out needs a full description at filing. The same logic applies in the United States, where a divisional must comply with section 120 to keep the original filing date.

Applicants can decide before filing which invention carries the commercial weight in each market, and order the independent claims so that the search report covers that invention first. The EPO searches the first-mentioned invention under Rule 64(1), and the first-mentioned group is the one covered by a partial report, so claim order has a direct effect there, and 37 CFR 1.476(c) provides the same first-mentioned rule where the USPTO is the Authority. For guidance on structuring independent and dependent claims, see types of patent claims and how they are structured.

The decision to make before the search report arrives is therefore concrete: identify which inventions in the claim set you would pay to have searched, or divide out, in India, Europe and the United States. If a further invention would not be pursued in any market, narrow the claims before filing and avoid the additional fee. If it would, keep the specification support and plan the divisional route in each office. For how the examination stage then plays out in India, see the guide to the first examination report in India.

Frequently Asked Questions

This article explains the law on unity of invention (with comparison to the PCT, EPC and US texts) in India as at October 2026 and is for general information only. It is not legal advice. Government fees, forms, and procedures change; confirm current figures with the Indian Patent Office before you file. For advice on your specific invention, consult a registered patent agent.

Sources

1. Regulations under the PCT (in force from 1 January 2026), Rules 13, 40, 43.7 and 68, WIPO. https://www.wipo.int/pct/en/texts/rules/r13.html
2. PCT International Search and Preliminary Examination Guidelines, paragraphs 10.03, 10.04 and 10.08 (https://www.wipo.int/pct/en/texts/ispe/10_01_10.html) and 10.12 to 10.16, WIPO. https://www.wipo.int/pct/en/texts/ispe/10_11_19.html
3. European Patent Convention, 17th edition (November 2020, with amendments to December 2023), Articles 76 and 82 and Rules 36, 44, 64, 137 and 164, European Patent Office. https://www.epo.org/en/legal/epc/2020/a82.html
4. Guidelines for Examination in the EPO, 2025 edition, Part F Chapter V section 3 (https://www.epo.org/en/legal/guidelines-epc/2025/f_v_3.html) and Part H Chapter II section 6.2 (Office practice), European Patent Office. https://www.epo.org/en/legal/guidelines-epc/2025/h_ii_6_2.html
5. 35 U.S.C. 121 (divisional applications), Legal Information Institute. https://www.law.cornell.edu/uscode/text/35/121
6. 37 CFR 1.499 (unity of invention during the national stage), Legal Information Institute. https://www.law.cornell.edu/cfr/text/37/1.499
7. 37 CFR 1.78, 1.141 to 1.146 and 1.475 to 1.477, and MPEP 802.02, 803, 804.01, 806.05(f) and 810 (Ninth Edition, chapter 800 at Revision 07.2022, February 2023) and 1893.03(d) (Revision 01.2024, November 2024), USPTO. https://www.uspto.gov/web/offices/pac/mpep/index.html
8. The Patents Act, 1970, sections 7, 10, 15, 16, 21, 25, 46, 64, 117A and 138 (text incorporating amendments till 1 August 2024), Government of India. https://www.indiacode.nic.in/bitstream/123456789/1392/1/A1970-39.pdf
9. The Patents (Amendment) Rules, 2024, G.S.R. 211(E), 15 March 2024, clause 3 (Rule 13(2A)), Gazette of India. https://ipindia.gov.in/pages/patents/rules-patents-2003
10. Manual of Patent Office Practice and Procedure, version 3.0 (2019), paragraphs 06.01.03, 07.02.07, 09.03.08 and 09.04 (Office practice), Office of the Controller General of Patents, Designs and Trade Marks. https://ipindia.gov.in/frontend/pdf/patents/Manual_for_Patent_Office_Practice_and_Procedure_.pdf
11. Syngenta Limited v Controller of Patents and Designs, C.A.(COMM.IPD-PAT) 471/2022, Delhi High Court (Division Bench), 13 October 2023, paragraphs 21, 25 and 32. https://indiankanoon.org/doc/195692430/