“Principal investigator” is a job title only in the loosest sense. It is really an accountability designation: the named individual on a grant, contract, or research protocol who is formally responsible for the science, the money, the ethics approvals, and the people doing the work. What that means in practice varies by field and institution, but the core job is consistent across an R01 lab, an NSF-funded engineering project, and a clinical trial site: the PI is the person everyone else, including the funder, holds accountable when something needs to be answered for.
This guide covers what a PI actually does across the life of a project — funding, scientific direction, budget, team leadership, compliance, and reporting — and how the role differs from adjacent titles like co-investigator, sub-investigator, and project manager. For the formal, compliance-focused definition of PI accountability (the version research administrators and IRBs work from), see CASRAI’s principal investigator (PI) dictionary entry. For how a PI applies project-management tools like work breakdown structures and Gantt timelines to a study, see Research Project Management for Principal Investigators — this guide is about what the role covers, not how to run the schedule.
Who Can Be a PI
PI status comes from award documentation, not job title or seniority alone. An early-career researcher can be the PI on a fellowship or a career-development award the same year a senior professor is PI on a multi-million-dollar program grant. In practice, though, most institutions and funders require a PI to hold a continuing (not purely temporary or trainee) position at the recipient institution, because the role carries obligations — effort certification, human-subjects oversight, records retention — that a short-term appointment can’t reliably guarantee. Some funders run explicit early-career PI tracks precisely to bridge this gap; see CASRAI’s guides to the K99/R00 Pathway to Independence Award, the NSF CAREER award, and early-career fellowships more broadly.
Multiple people can share the PI role on one award. NIH’s Multiple Principal Investigator (Multiple PD/PI) option, in place since 2006, lets an application name more than one PD/PI, each individually and fully accountable — naming additional PIs does not dilute any one person’s responsibility. Multiple-PI applications must include a Leadership Plan describing how governance, decision-making, and publication credit will be handled among the co-PIs, and one PI is designated the Contact PI as the funder’s single point of contact. This is a different arrangement from a co-investigator or sub-investigator, who contribute substantively to the work but are not the accountable party of record; see Co-Investigator vs. Co-PI and Principal Investigator vs. Sub-Investigator for how those roles compare.
Core Responsibilities
Across funders and fields, a PI’s responsibilities cluster into six areas. None of them is optional, and most are non-delegable in the sense that the PI remains accountable even when specific tasks are carried out by other staff.
1. Securing and Sustaining Funding
Someone has to write the proposal, and that’s usually the PI: framing the research question, justifying the budget, and making the case to a funder or reviewer panel that the work is worth paying for. See CASRAI’s guide to writing a grant proposal for the mechanics. Funding responsibility doesn’t end at award: a PI typically also manages no-cost extensions, competitive renewals, and, when a project’s direction genuinely changes mid-course, discussions with the program officer about scope.
2. Scientific and Technical Direction
The PI sets and is accountable for the intellectual direction of the work: the research design, whether the methods described in the approved application are actually being followed, and what gets reported as the result. Under the NIH Grants Policy Statement, the Program Director/PI is explicitly responsible for the scientific and technical conduct of a project. On an award with Multiple PD/PIs, each named PI carries this responsibility individually, not as a shared, diffused obligation.
3. Financial Stewardship
Day-to-day budget management sits with the PI: keeping spending aligned with the approved budget, justifying re-budgeting when priorities shift, and certifying that costs charged to the award are allowable, allocable, and reasonable. On federally funded projects this extends to effort certification — confirming that the percentage of committed time charged to an award reflects work actually performed, covered in detail in CASRAI’s guide to effort-reporting methodologies. The recipient institution, through its Authorized Organizational Representative, holds the underlying legal and financial accountability to the funder, but the PI is the one making the operational calls.
4. Team Leadership and Supervision
PIs supervise the study or lab team — co-investigators, postdocs, graduate students, and research staff — which means more than assigning tasks. It includes making sure each person is qualified and appropriately trained (human-subjects protections, biosafety, financial-conflict-of-interest disclosure), mentoring trainees toward their own independence, and being able to demonstrate, if asked by a funder or IRB, that delegated work was actually overseen rather than just nominally signed off. Where a project has designated Senior/Key Personnel beyond the PI, the PI is typically the one coordinating their training and reporting obligations too.
5. Ethics and Regulatory Compliance
Where a project involves human participants, animal subjects, or biological/chemical hazards, the PI is responsible for obtaining the required approval before work begins — from an Institutional Review Board (IRB), Institutional Animal Care and Use Committee (IACUC), or equivalent — and for keeping that approval current through amendments and continuing review. In an FDA-regulated clinical trial, the site PI personally signs FDA Form 1572, a direct commitment to the agency under 21 CFR 312.60 to conduct or supervise the study as approved, obtain informed consent from every subject, report adverse events, and maintain accurate records. This obligation exists independently of whatever the site’s contract with the sponsor says.
6. Reporting to the Funder
Reporting cadence is set by the funder, not the project team. Most NIH awards require a periodic Research Performance Progress Report (RPPR), submitted through eRA Commons on a schedule fixed at the time of award regardless of where the science actually stands; NSF uses the same RPPR terminology through Research.gov. A PI who only tracks internal project milestones and ignores the funder’s reporting calendar will regularly be caught off guard by a report deadline.
PI vs. Related Roles
“Principal investigator” gets used loosely in conversation to mean “the person in charge,” which blurs it with several distinct, more specific roles. The table below separates them by who holds formal accountability to the funder or regulator.
| Role | What distinguishes it from PI |
|---|---|
| Co-PI (Multiple PD/PI) | Shares full, individual PI accountability on the same award — not a lesser role, a parallel one. See Co-Investigator vs. Co-PI. |
| Co-investigator | Contributes substantively to the science but is not the accountable party of record; the co-investigator role is typically named in the application without carrying the PI’s compliance and reporting obligations. |
| Sub-investigator | In clinical trials, performs delegated study procedures under the PI’s supervision but does not sign FDA Form 1572. See Principal Investigator vs. Sub-Investigator. |
| Research administrator | Manages the institutional pre-award and post-award processes (proposal routing, compliance paperwork, award setup) that support the PI’s project, rather than directing the science itself. See What a Research Administrator Does. |
| Project manager | On larger or multi-site studies, may own the day-to-day schedule and coordination the PI doesn’t have time for, but does not hold the PI’s regulatory and funder accountability. See Research Project Management for Principal Investigators for how PIs use PM tools directly when there’s no separate PM role. |
How Someone Becomes a PI
There’s no single credential that confers PI status — it’s a function of institutional eligibility policy plus, usually, a track record of independent research output. The typical path runs through a postdoctoral or early-faculty stage, during which a researcher builds the publication record and preliminary data needed to compete for their own funding, then transitions to PI status on a career-development or independent-research award. Common on-ramps include:
- An institutional appointment (tenure-track faculty, research-track scientist, or equivalent continuing position) that satisfies the host institution’s PI eligibility policy.
- A career-development mechanism explicitly designed for the transition, such as the NIH K99/R00 Pathway to Independence Award, an NIH K-series career development award, or the NSF CAREER award for early-career faculty.
- A funder-specific early-career PI track, such as those covered in CASRAI’s early-career fellowships guide.
Some institutions grant PI eligibility case by case — for example, allowing a research scientist or a fellow with demonstrated independence to serve as PI on a specific mechanism even without a standard faculty appointment. Because this varies by institution, the eligibility answer for any specific person is ultimately whatever the sponsored-programs or research-administration office says it is, not a fixed rule.
What a PI Does Beyond the Formal Job Description
The compliance-and-accountability list above is what a PI is answerable for. Day to day, the job also includes work that doesn’t show up in any regulation: writing and revising manuscripts, presenting at conferences, reviewing for journals and grant panels, building and maintaining collaborations, and mentoring trainees toward their own careers — including writing the letters of reference and research statements that help those trainees become PIs themselves. None of this is separately regulated, but it’s a large share of what fills a PI’s actual working week, and it’s the part of the role that’s hardest to delegate because it depends on the PI’s own scientific judgment and professional standing.
Frequently Asked Questions
Does a PI have to be a professor?
No. PI eligibility is set by institutional policy and typically requires a continuing appointment, but that can include research-track scientists, some senior fellows, and non-faculty investigators at research institutes, hospitals, and independent labs — not only tenure-track faculty.
Can a postdoc be a PI?
Usually not on a standard institutional appointment, but yes on mechanisms designed for the transition, such as an NIH K99/R00 award, where the K99 phase itself is typically mentored, and independent PI status begins at the R00 phase once the recipient has moved to a qualifying faculty or research-track position.
What’s the difference between a PI and a co-PI?
Under NIH’s Multiple PD/PI model, a co-PI is not a subordinate role — each named PI on a Multiple PD/PI award is individually and fully accountable for the project, with a Leadership Plan defining how they divide governance and decision-making. “Co-PI” outside NIH terminology is sometimes used more loosely to describe a secondary PI role with less formal standing; the exact meaning depends on the funder and the award documentation.
Is a PI the same as a project manager?
No. A PI holds the funder-facing scientific, financial, and regulatory accountability for a project; a project manager (where one exists on a study) typically owns schedule and coordination. Many research projects never have a separate project manager at all — the PI absorbs that function directly, which is the scenario covered in CASRAI’s Research Project Management for Principal Investigators guide.
Who is accountable if a PI delegates a task and it’s done wrong?
The PI, in most cases. Funders and IRBs generally treat PI responsibilities as non-delegable in substance: an institution can assign specific tasks to named staff, but the PI remains the accountable party of record. This is stated explicitly for FDA-regulated trials under 21 CFR 312.60, and reflected more generally in the NIH Grants Policy Statement’s treatment of PD/PI accountability.
References
- NIH Grants Policy Statement, Section 2 (Recipient Staff / PD-PI responsibilities) — grants.nih.gov
- NIH Multiple Principal Investigator (Multiple PD/PI) policy and Leadership Plan requirement — grants.nih.gov
- 21 CFR 312.60 — General Responsibilities of Investigators
- FDA Form 1572 (Statement of Investigator) and accompanying instructions
- NIH/NSF Research Performance Progress Report (RPPR) guidance — era.nih.gov, research.gov
