Co-Principal Investigator: NIH vs. NSF Roles

“Co-principal investigator” is one of the most inconsistently used titles in federal research administration, because it means three genuinely different things depending on who is using it. NIH does not formally recognize a “co-PI” title at all — it uses a Multiple Program Director/Principal Investigator (Multiple PD/PI) model in which every named individual is a co-equal PI, not a subordinate “co.” NSF, by contrast, has an explicit co-PI role on its proposal cover sheet, distinct from the PI and from senior/key personnel, with its own eligibility limits. Separately from either agency’s formal usage, institutions routinely use “co-PI” as an internal, informal label for credit or workload-sharing purposes that carries no meaning to a federal sponsor whatsoever. A researcher who has only encountered one of these three usages will misread documents built around either of the other two — and the title on a business card, CV, or promotion dossier does not tell you which one applies. This guide untangles all three, then walks through what each designation actually changes on the award itself.

The three meanings of “co-PI,” side by side

Before going through each usage in detail, here is how they compare on the dimensions that actually matter for compliance, credit, and reporting.

Dimension	NIH Multiple PD/PI	NSF Co-PI	Senior/Key Personnel	Informal institutional “co-PI”
Is “co-PI” a real title here?	No — NIH names multiple PDs/PIs, each a co-equal PI; there is no separate “co-PI” rank beneath them	Yes — a distinct, named role on the proposal cover sheet	No — a broader category that PIs and co-PIs both fall inside	Sometimes, but with no fixed definition — varies by department/institution
Governing framework	Multiple PD/PI policy, established via NOT-OD-07-017 (2006)	NSF Proposal & Award Policies & Procedures Guide (PAPPG), Exhibit II-3	Defined in the same PAPPG exhibit; also an NIH eRA/biosketch category	None — department or school convention only
Required governance document	Leadership Plan, submitted with the application and factored into scientific review	Not required in the same form; role is declared on the cover sheet	Not applicable	Not applicable
Accountability to the sponsor	Full, shared accountability — every named PD/PI is accountable for the project as a whole	Substantive scientific responsibility, but NSF’s award relationship runs through the single named PI	Contribute in a substantive, measurable way to scientific development or execution, but are not necessarily accountable for the whole project	Undefined — depends entirely on local practice
Numeric limit	No fixed cap; institutions and reviewers expect the number to be justified by genuine shared leadership need	PAPPG Exhibit II-3: one PI plus up to four Co-PIs per proposal	No cap on Senior/Key Personnel as a category	No limit — and no external body would enforce one
Point of contact with sponsor	One designated Contact PI, who must be affiliated with the applicant organization	The single named PI remains the sponsor’s point of contact	Not applicable	Not applicable
Where it appears officially	Notice of Award, eRA Commons, RPPR	NSF award notice, Research.gov	Biosketch/Current and Pending Support disclosures, research-security certifications	CV, promotion dossier, department records only — never the award document

NIH: there is no formal “co-PI” — there is Multiple PD/PI

NIH established the Multiple Principal Investigator option through NOT-OD-07-017, published November 20, 2006, following a 2006 pilot phase, with the option available to applications submitted for the February 2007 receipt dates onward. Under this model, an application can name more than one Program Director/Principal Investigator, and NIH treats each named PD/PI as a full, co-equal principal investigator — not as a “PI” plus one or more subordinate “co-PIs.” The distinction is not just semantic: NIH’s own guidance and policy statement never use “co-PI” as a defined role. When someone says “I’m a co-PI on an NIH award,” what they usually mean is that they are one of several named PD/PIs under the Multiple PD/PI model — and under that model, they carry the same formal accountability as every other named PD/PI, not a lesser one.

Two structural requirements come with choosing this model:

A Leadership Plan is required whenever an application names more than one PD/PI. NIH reviewers factor the plan into the overall scientific merit assessment — it is not a pro forma administrative attachment. It must address the rationale for a multi-PI approach, the governance and decision-making structure, each PD/PI’s role and area of responsibility, budget/resource allocation, and how data-sharing and publication decisions will be handled and disputes resolved.
One PD/PI must be designated the Contact PI — NIH’s single administrative point of contact for the award. The Contact PI must be affiliated with the applicant organization submitting the application. This is a coordination and communication designation, not a hierarchy: the Contact PI does not carry more scientific authority, more accountability, or more credit than the other named PD/PIs. It exists so NIH has one routing address for programmatic correspondence, not so the team has a lead scientist by another name.

For the full mechanics of what a Leadership Plan must contain and when NIH requires one, see CASRAI’s guide to the NIH Multiple PD/PI Leadership Plan.

NSF: co-PI is a real, distinct, capped role

NSF’s usage is the inverse of NIH’s: the agency’s Proposal & Award Policies & Procedures Guide (PAPPG) — the current in-force edition being PAPPG NSF 24-1 — explicitly defines Senior/Key Personnel (PAPPG Exhibit II-3) as falling into two categories: (co-)PI and Faculty Associate. Within the (co-)PI category, a proposal may name one PI plus up to four Co-PIs. Both roles are declared on the proposal cover sheet, and NSF’s system distinguishes them structurally from other Senior/Key Personnel, who contribute substantively to the project but are not named PI or co-PI.

NSF does not require a Leadership Plan analogous to NIH’s, and the named PI (not a rotating or shared contact role) remains NSF’s primary point of contact for the award. Co-PI status at NSF is real and carries genuine scientific responsibility, but it does not create the same fully co-equal, jointly-accountable structure that NIH’s Multiple PD/PI model does — the two agencies built genuinely different governance models around superficially similar-sounding titles.

Co-PI eligibility is not unconditional across every NSF mechanism. The CAREER program is a documented example: NSF’s own CAREER FAQ lists a co-PI on the cover page as one of the explicit triggers for return without review — CAREER awards are single-PI by design. Always check the specific solicitation rather than assuming PAPPG’s general co-PI allowance applies everywhere.

Senior/key personnel: broader than co-PI, and not the same category

Both agencies use a category above and around the PI/co-PI distinction: Senior/Key Personnel. NIH defines Senior/Key Personnel as the PD/PI plus any other individual who contributes to a project’s scientific development or execution in a substantive, measurable way, regardless of salary support — a narrower group than everyone named in the application, but broader than the PD/PI(s) alone. NSF’s PAPPG Exhibit II-3 uses a parallel structure, with (co-)PI as one of two Senior/Key Personnel categories (the other being Faculty Associate).

The practical distinction that trips people up: every co-PI is Senior/Key Personnel, but not every Senior/Key Personnel is a co-PI. A named co-investigator, consultant with a substantial role, or key collaborator can be Senior/Key Personnel — subject to biosketch, Current and Pending Support disclosure, and (increasingly) research-security training and certification requirements — without holding PI or co-PI status on the award at all. Titles like “co-investigator” are commonly used for this tier; see CASRAI’s Co-Investigator vs. Co-PI comparison for how that specific pairing is distinguished.

Informal institutional “co-PI”: real for credit, meaningless to the sponsor

A third usage exists alongside the two formal ones: departments, schools, and individual researchers frequently use “co-PI” as an internal shorthand for someone who contributed substantially to a project’s leadership without necessarily being named PI or PD/PI on the actual award documents — often for annual review, tenure and promotion, or internal credit-allocation purposes. This usage has no agency definition behind it and does not appear on a Notice of Award, in eRA Commons, or in Research.gov. It can be entirely legitimate as an internal institutional practice, but it is not interchangeable with either of the two formal usages above, and using it in a way that implies formal co-PI or Multiple PD/PI status to a sponsor (in a biosketch, in effort certification, or in a compliance disclosure) is a real error, not a stylistic choice. If in doubt about which usage applies to a specific document, check the award’s own title/role fields rather than what someone’s business card or CV says.

2 CFR 200.1: no federal definition of “principal investigator” to fall back on

It is worth being explicit about a gap researchers sometimes assume is filled: 2 CFR Part 200 (the Uniform Guidance that governs federal grants generally) does not define “principal investigator” or “co-principal investigator” as terms in its 200.1 definitions section. There is no single, government-wide regulatory definition of the PI or co-PI role to appeal to across agencies — each funding agency (NIH, NSF, and others) defines the role, and any co-PI equivalent, in its own policy guidance (the NIH Grants Policy Statement and PAPPG respectively). That absence is precisely why the same title means different things depending on which agency’s award you are looking at, and why the institutional policy or PI-eligibility rules that do exist at most universities are locally written, not federally mandated.

Where each designation actually shows up

The label matters less than what it changes in practice. Here is where each of the formal designations has a real, documented effect:

Notice of Award (NIH) / award notice (NSF): the official, legally binding award document names every PD/PI (NIH) or PI/co-PI (NSF). This is the authoritative record of who holds the role — not a biosketch, CV, or internal title.
Effort reporting: under 2 CFR § 200.430, any individual with committed effort on a federal award — PD/PI, co-PI, or other Senior/Key Personnel — must certify that effort, regardless of which of the three “co-PI” usages above applies to them informally. The effort-certification obligation tracks committed effort, not title.
RPPR (NIH’s Research Performance Progress Report): only the PD/PI or their delegate can initiate an RPPR. On a Multiple PD/PI award specifically, only the Contact PD/PI or the Contact PD/PI’s delegate can initiate it — the other named PD/PIs cannot, even though they hold equal formal accountability for the project. Only a Signing Official can actually submit the completed RPPR to NIH.
Research-security and Senior/Key Personnel certifications: NSF and NIH have both layered research-security training and certification requirements (e.g., NSF’s annual MFTRP certification, NIH’s Senior/Key Personnel research-security training requirement) onto the PI/co-PI/Senior-Key-Personnel population specifically — these obligations attach based on formal role, not informal institutional title.
Institutional credit and promotion cases: this is the one place where the informal, third usage of “co-PI” does real work — department and tenure committees routinely credit “co-PI” contributions that never appeared as a formal designation on any award document. That is a legitimate internal practice, but it is worth naming explicitly in a CV or dossier as institutional/internal usage rather than implying it maps onto a specific agency’s formal role, since a reviewer familiar with NIH or NSF policy may otherwise misread the claim.

Co-PI role versus authorship on a resulting paper

A separate confusion worth flagging directly: holding a PI or co-PI role on the grant that funded a project is a distinct question from earning authorship on the papers that project produces. Grant roles are administrative/accountability designations defined by a funding agency’s policy; authorship is defined by the norms of the journal and field (commonly operationalized today through the CRediT Contributor Roles Taxonomy, which enumerates specific contribution types such as conceptualization, funding acquisition, or supervision). A PI’s grant role does not automatically confer authorship, and conversely, someone can be a substantial contributing author without ever having held a PI or co-PI role on the funding award. CASRAI covers this distinction in more depth in Principal Investigator vs. Author: Does the PI Role Confer Authorship?

Frequently asked questions

Is “co-principal investigator” an official NIH title?

No. NIH’s formal model is Multiple PD/PI, in which every named individual is a co-equal Program Director/Principal Investigator. NIH policy does not define a subordinate “co-PI” role beneath the PD/PI(s); people use “co-PI” informally to describe being one of several named PD/PIs, but the underlying NIH designation is equal PD/PI status, not a lesser co-PI tier.

How many co-PIs can an NSF proposal have?

Under PAPPG Exhibit II-3, an NSF proposal may name one PI plus up to four Co-PIs. Individual program solicitations can impose tighter limits or, as with the CAREER program, bar co-PIs entirely — always check the specific solicitation.

Does being a co-PI on a grant make someone an author on the resulting paper?

Not automatically. Grant roles and paper authorship are governed by different norms — a PI or co-PI role reflects agency-defined accountability for the award, while authorship reflects the journal/field’s contribution criteria (see CRediT). The two frequently overlap in practice but are not the same determination.

Who is the Contact PI, and does that role outrank the other PD/PIs?

The Contact PI is NIH’s single designated point of administrative contact on a Multiple PD/PI award and must be affiliated with the applicant institution. It is a communication/coordination role, not a hierarchy — every named PD/PI, including the Contact PI, carries the same formal accountability for the project under NIH’s Multiple PD/PI model.

Can someone be Senior/Key Personnel without being a co-PI?

Yes. Senior/Key Personnel is the broader category: it includes the PI/PD-PI(s) and co-PI(s) but also anyone else contributing substantively and measurably to the project’s scientific development or execution — co-investigators, key collaborators, and certain consultants can be Senior/Key Personnel without holding PI or co-PI status on the award itself.

Co-Principal Investigator: What the Title Means at NIH, NSF, and Your Institution

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