While many scientists use terms such as "Collaborator" and "Co-investigator" interchangeably, the NIH has specific definitions for these terms as well as other terms used to define roles and responsibilities for individuals associated with grants.  It's important that the correct term is used to convey the lead PI's intentions of how individuals are anticipated to contribute to the work proposed as well as what documents are needed at the point of submission. This can significantly impact how a grant is scored. It also impacts how indirect costs are distributed within the University after a grant is received, and who is considered responsible for reporting, compliance, and other aspects of managing the awarded grant.

For the following discussion, it is helpful to break down grants into 3 types. The first type are grants made to individual investigators (F32, K01, K99) or research projects (R01, R21). The second type includes large consortium grants (P01, U01). The third type are training grants (T32, R25, R38). individual investigator grants, particularly R01 grants, are where people usually experience the most confusion.

PD/PI

All grants are required to have someone listed as the "Program Director/Principal Investigator (PD/PI)". For a fellowship or other traineeship award (F32, K01, K99, etc), this role is occupied by the graduate student or postdoctoral fellow applying for the award, and this individual is most commonly the only person listed as "key personnel" on the application. In the case of an R01 where a faculty member intends to individually perform the proposed research within his or her lab using only his or her staff and trainees, the faculty member is listed as PI, and usually no other key personnel are listed.

Multi-PI grants are R01 grants where the research proposed requires a "team science" approach. Here, responsibility and credit for the grant are shared between 2 or more individuals who can be at the same or different institutions (which impacts distribution of indirect costs). The project scope is such that the group of PIs working together are required to achieve all aims; no individual PI is capable of running the project independently, and all PIs on a multi-PI grant are considered key personnel.

To summarize, for a "standard" R01 written by a single faculty member who intends to complete the project aims within their lab, the faculty member should be listed as the PD/PI, and will likely be the only "key personnel" included in the application and, if the grant is awarded, listed on the Notice of Award. Other faculty completing supporting activities or providing resources are not listed as key personnel. They contribute Letters of Support, which the PI references within the Research Strategy and other relevant sections of the grant. Individuals providing services, who are also not key personnel, should be listed as consultants and included in both the budget and budget justification.

Supporting faculty with no role

If the faculty member requires support from another faculty member to complete the aims, but that support  does not confer any authority or responsibility to the supporting faculty member, generally all that is required is for the supporting faculty member to write a "Letter of Support" to include with the grant submission. For example, subaim 2.1 of an R01 proposal requires use of a specific mass spectrometer. The faculty who will be PI on the grant, Dr. Primary, does not have this equipment, however their colleague, Dr. Spec, does have the needed machine in his lab, and has indicated that he is happy to let Dr. Primary use his machine, and that he will help train one of Dr. Primary's postdocs to use it. In this case, Dr. Primary, when writing subaim 2.1 of her grant proposal, would mention that she already has access to the necessary equipment via Dr. Spec, and include the text (See LOS). Dr. Spec would provide Dr. Primary with a simple letter noting that Dr. Primary was welcome to use his machine. With this setup, no amount of the submitted budget would be committed to Dr. Spec, and Dr. Spec would have no authority or responsibility for the execution of the aims of the proposal, reporting, or any other aspects of the grant. Effectively, Dr. Spec is doing a favor for Dr. Primary.

Consultants

In rare cases, a PI might require help to complete grant objectives from an outside expert, often an employee of a company, on a fee for service basis. Individuals in these roles have no authority or responsibility for a grant, and would not be listed as authors on any resultant publications. The relationship is very transactional. For example, subaim 3.1 of Dr. Primary's grant proposal includes analysis of blood samples for specific vitamins and minerals. Dr. Primary's university doesn't have a facility that provides these services. Dr. Primary finds a company, Vitamin Analytics that will allow her to hire a vitamin expert on an hourly basis to analyze the blood samples and report on the levels of the desired vitamins.  In this case Dr. Primary should list costs associated with using the services provided by the staff at Vitamin Analytics under consulting on her budget, and detail the nature of the services and anticipated associated costs in her budget justification.

Other Personnel

The next set of personnel to address are the postdocs, graduate students, and research staff required to complete the aims of the proposed research. Communicating that personnel are in place  to complete the proposed research project is essential for the success of a grant proposal. 

The place to do this is on both the budget and the budget justification. As line items in an itemized budget,  list the names of lab members involved in the project, their role (postdoc, graduate student, tech, etc) and their %FTE. Your Research Administrator can then calculate out the dollar amount of salary and benefits this corresponds to for each individual. These same individuals should then be listed on the budget justification with a brief description of their experience, and how this experience will facilitate their ability to complete the objectives assigned to them on this grant, effectively establishing to reviewers that the PI has a team in place to complete the research aims. 

Please note that these people should NOT be included as "key personnel", regardless of how important a specific individual is to the research project. The rationale for this is that the NIH requires prior approval to remove or change anyone listed as "key" on the Notice of Award, as these individuals were deemed to be essential to the success of a specific research program. If, for example, a postdoc listed as "key personnel" were to accept a faculty position in Y2 of a 5 year grant, the PD/PI would essentially have to "prove" that they had someone else capable of fulfilling the obligations of that person in order to retain the grant. This is something best avoided, particularly in cases where multiple lab members have overlapping skillsets and a graduate student, for example, would be able to complete the tasks of the former postdoc.

Occasionally, particularly for new faculty members, a PI may not have a specific individual to list in one of the positions required to complete the grant. In this case, on the budget use "to be named" as the name of the individual, and then include %FTE and anticipated salary and benefits costs. Then, in the budget justification, describe how you will find a person to fulfill this role. If for example, you are in the process of hiring a technician, you can include language to the effect of "we are currently interviewing technicians, all of whom have experience in the necessary technologies to complete the aims of the proposal, for this role. We anticipate that we will have an employee in place by the scheduled start date of the grant".