I notice that some schools, e.g., MIT EECS, has these two non-faculty appointments, Principal Research Scientist and Senior Research Scientist.

At least true for MIT EECS:

Both of them, just as Faculty members, are PI's and can run their own research groups. One difference I know is that Principal Research Scientist's appointment is reviewed every 4 years, whereas Senior Research Scientist's is evaluated every 5 years (as per MIT's website). Yet, this doesn't tell much.

In addition, Principal Research Scientist falls under "Sponsored Research Staff Appointments" category, whereas Senior Research Scientist falls under "Academic Research Staff Appointments". Does this tell something?

What is the exact difference between them and the Faculty members (i.e., professors)?

Why aren't they just called professors?

What are the differences between these two?

  • 2
    It sounds like the Senior Research Scientist position is just slightly higher up the ladder than Principal Research Scientist. But neither position has tenure, which is why they're different from professorships (they might also differ in salary and teaching obligations).
    – Moriarty
    Commented Oct 30, 2014 at 14:11
  • 2
    The probably aren't called professors since they likely have no teaching responsibilities.
    – Bill Barth
    Commented Oct 30, 2014 at 14:11
  • 4
    "Principal XY" is typically a higher rank than "Senior XY". Maybe you got it in the wrong oder?
    – xLeitix
    Commented Oct 30, 2014 at 14:15
  • @xLeitix No, I didn't get it wrong. I actually feel the same as you. But see 5.2.1 and 5.3.1 web.mit.edu/policies/5/5.2.html Commented Oct 30, 2014 at 15:42
  • I can't say for sure, but the word "sponsored" appearing in one and not the other makes me wonder if maybe the sponsored position is funded entirely by external grants and the other involves some salary paid by the university. That's just a guess, though.
    – Matt Reece
    Commented Oct 30, 2014 at 15:46

3 Answers 3


According to the MIT EECS pages, there are two tracks:

  • Academic Research Staff. These are mostly shorter term (such as a Postdoctoral Fellow), and are funded externally (by grants and similar).
  • Sponsored Research Staff. These are longer term appointments which are funded by the department.

Senior Research Scientist is an Academic Research Staff position, because while it is long-term, it is also a position for which the researcher is expected to procure their own funding.

From 5.3, the SRS's funding:

Appointees to this rank generally are expected to raise funds to conduct research and cover their own salaries.

Principal Research Scientist is a Sponsored Research Staff position, and is funded by the department (though I'm sure they can get their own funding also, their salary is paid by the department).

From 5.2, the PRS's funding:

Funding responsibility resides with the department, laboratory, or center that is the locus of the appointment.

From 5.1 on the difference:

Two types of research appointments are described in the following sections: long-term appointments, which are classified as sponsored research staff appointments, with the exception of the Senior Research Scientist/Associate/ Engineer position; and short-term appointments, which are, in general, classified as academic research appointments.

The purpose of the campus research appointment structure is to create professional sponsored research staff categories with employee benefits and privileges in order to encourage long-term research careers at MIT. The concept of long-term professional careers, independent of classroom teaching and supported entirely from research grants, is not a new one for the American research university. This mode of research, with professionals working in departments, laboratories, and centers, is an important mechanism for universities to maintain research viability, enter new fields, and bring researchers to the campus.

It seems evident that Senior RS is basically the same position as PRS, but not funded by the department. In some cases, the PRS could earn more, because (for example) a NIH-funded SRS would be limited by NIH regulations, while a PRS who is funded by the department is only limited by whatever MIT chooses to pay them.


For scientists,there are "Research Scientist", "Principal" and "Senior". The latter two can be PIs. The later two also have short term tenure meaning the university will cover their pay for a short term should their funding lapse. I believe for Senior it is one year. Senior are equivalent of full professors in rank and help set the research direction of the whole lab or group. Principals can seek and run their own grants and may or may not have some departmental funding if the dept has large support grants.

Senior is definitely a bigger deal than Principal. There is a big salary step to senior. At MIT Senior is limited to 10% of faculty and principal to 15%. Scientists don't have to teach or have grad students and have no "tenure clock". you will typically find them at larger research groups and labs that have dozens if not over a hundred staff and students.


In many U.S. institutions, MIT EECS being one example, there are parallel Professor and Research Scientist career tracks. Typically, they compare as follows:

  • Professors are required to teach, supervise students, are always primary investigators, can gain tenure, and have 9-month salary paid by the department, with summer pay dependent on external funding.
  • Research Scientists are not required to teach (though they often do, particularly graduate seminars), sometimes supervise students, are sometimes primary investigators, cannot gain tenure, and all of their pay is dependent on external funding.

Both tracks have rank denoted by adjective (e.g., "Assistant, Associate, [], XXX Chair" for a professor). Typically 'Principal' is higher than 'Senior'---the numbers on the MIT EECS pages look to imply the opposite of that, but I am not certain.

  • the numbers on the MIT EECS pages would tend to confirm that? Principal is renewed every 4 years, and Senior every 5 years. Shouldn't Senior sound higher here? :) Commented Oct 30, 2014 at 15:46
  • 1
    @FarticlePilter Actually, I got the numbers backward; on csail.mit.edu/biographies/PI/biolist.php there are 10 Principals and 4 Seniors. I will edit.
    – jakebeal
    Commented Oct 30, 2014 at 15:52

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