Co-Investigator: How the Role Differs from PI

Co-investigator

A named investigator on a research grant, contract, or protocol other than the lead PI, who contributes substantive scientific expertise and shares responsibility for portions of the work, typically with a defined role in the proposal and a named budget allocation.

ByCASRAI Editorial Board

· Last updated 15 Aug 2026

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Co-investigator status carries scientific responsibility but not the lead-PI’s ultimate accountability for the whole project. The role is distinct from collaborator (who provides resources or input but has no formal responsibility) and from consultant (who advises against a fee).

References

NIH Multiple Principal Investigator Policy
UKRI Co-Investigator Eligibility

Frequently Asked Questions

What is a co-investigator in research?

A co-investigator is a named investigator on a research grant, contract, or protocol — other than the lead principal investigator (PI) — who contributes substantive scientific expertise and shares responsibility for part of the work, typically with a defined role in the proposal and a named budget allocation.

Does a co-investigator carry the same accountability as the principal investigator?

No. A co-investigator carries scientific responsibility for their portion of the project, but not the lead PI’s ultimate accountability for the project as a whole.

What is the difference between a co-investigator and a collaborator?

A co-investigator has a formally defined role and budget allocation on the grant and shares scientific responsibility for part of the work. A collaborator, by contrast, provides resources or input to the project but has no formal responsibility — for example, someone who supplies a unique reagent but isn’t named on the grant is a collaborator, not a co-investigator.

How does a co-investigator differ from a consultant?

A consultant advises on a project in exchange for a fee, but does not hold the scientific responsibility or formal named role that a co-investigator has.

Are “co-PI” and “co-investigator” the same thing?

CASRAI lists “Co-PI” and “Co-I” as aliases for co-investigator, so the terms are often used interchangeably in practice. Usage can still vary by funder and institution, so it is worth checking the specific policy that applies to a given grant.

Use in your systems

JATS XML <role> element

xml

<role vocab="credit"
      vocab-identifier="https://casrai.org/dictionary/"
      vocab-term="Co-investigator"
      vocab-term-identifier="https://casrai.org/dictionary/term/co-investigator" />

Schema.org DefinedTerm (JSON-LD)

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