Direct comparison
Co-Investigator vs. Co-PI
Co-PI (NIH Multiple PI model) means co-equal, shared authority. Co-Investigator means real but bounded responsibility. See how budget/effort rules differ.
Side-by-side comparison
| Dimension | Co-Investigator | Co-PI (NIH Multiple PI model) |
|---|---|---|
| Accountability to sponsor | Substantive scientific responsibility for a defined portion of the work; not ultimately accountable for the project as a whole | Full, shared accountability for the entire project, jointly with the other named PI(s) |
| Governing model | Traditional single-PI model — the default structure absent a formal multi-PI policy | NIH Multiple Principal Investigator (Multiple PD/PI) policy, adopted November 2006 |
| Required governance document | None required | Leadership Plan required in the application, describing governance, decision-making, and conflict resolution |
| Point of contact with sponsor | Routed through the lead PI | One designated Contact PI (must be affiliated with the applicant institution) communicates with NIH on the team's behalf |
| Budget authority | Named budget line for their own workstream; no control over the overall award budget | Shares programmatic and budgetary authority as defined in the Leadership Plan |
| Effort reporting / certification | Required per 2 CFR § 200.430 for any committed effort | Required per 2 CFR § 200.430 for any committed effort — same obligation, applied to every named PI |
| Recognized by NSF? | Yes — NSF's standard term for additional senior personnel beyond the PI | NSF allows a Co-PI on most standard proposals but has no formal joint-accountability framework equivalent to NIH's; some mechanisms (e.g. CAREER) bar Co-PIs entirely |
| Recognized by UKRI? | Yes — UKRI's standard term for named research staff beyond the lead PI, without a Multiple-PI-style model | Not a distinct formal UKRI category; UKRI grants use "Co-Investigator" for this role |
| Can be at a different institution? | Yes, commonly, especially on collaborative or multi-institutional awards | Yes, but the designated Contact PI must be affiliated with the applicant organization submitting the award |
Common questions
FAQ
Is "Co-PI" always the same as "Co-Investigator"?+
No. Under NIH's formal Multiple Principal Investigator policy, a Co-PI is a co-equal PI with shared ultimate accountability — a distinct, higher standing than a Co-Investigator. But many institutions and funders outside that specific NIH framework use "Co-PI" loosely as a synonym for Co-Investigator. Always check the specific funder's policy and the actual award document rather than assuming from the label alone.
Does NIH require a Leadership Plan for every multi-PI application?+
Yes. Every application naming multiple PD/PIs must include a Leadership Plan describing the governance structure, decision-making process, and how the team will resolve conflicts — it is a required part of the research plan, not optional documentation.
Do Co-Investigators need to certify effort the same way PIs do?+
Yes. Effort certification under 2 CFR § 200.430 applies to anyone with committed effort charged to a federal award, regardless of whether they are the lead PI, a Co-PI, or a Co-Investigator. The Multiple PI distinction affects programmatic authority and accountability, not whether effort reporting is required.
Can a project have more than two Co-PIs?+
Under NIH's Multiple PI policy, yes — there is no fixed cap on the number of PDs/PIs named, though institutions and study sections generally expect the number to be justified by the scope and complexity of the project, and the Leadership Plan has to meaningfully address governance for however many are named.
Which PI does a sponsor hold responsible if something goes wrong?+
Under a traditional single-PI structure, the lead PI. Under NIH's Multiple PI model, every named PI is jointly accountable — that shared accountability is the entire point of the policy, and is why the Leadership Plan is a required part of the application rather than a formality.
