I worked in a research group and now I am applying to a PhD program. A positive reference letter, especially the one from the big-named Principal Investigator (PI, project leader), will be very helpful.

My direct supervisor was a Research Scientist instead of a professor (PI). The professor (PI) of our group knows me, but not very well, since he has dozens of Postdocs and dozens of students to take care of. So I am think about having my direct supervisor write the letter and having the PI to co-sign.

However I've heard that two people signing a single reference letter is extremely uncommon is US. Not sure what is my best option.

  • 2
    Ask for two letters, one from the Reasearch Scientist, and one from the PI. Ask the Research Scientist to give the PI feedback to help him write a strong recommendation.
    – Anon
    Nov 5, 2018 at 9:32
  • 1
    @Anon Asking for two is a very good idea but I am allowed to submit a maximum of three letters. One must be the current supervisor and the other must be from undergrad, leaving one "free" spot of letters left.
    – High GPA
    Nov 5, 2018 at 12:17
  • One possible issue with two signatures on a letter is that the receiver might interpret it as if it were two letters already. Unless you know that isn't the case, tread carefully here. Whether it is uncommon or not, only the single current situation affects you.
    – Buffy
    Nov 5, 2018 at 13:37

1 Answer 1


So, as suggested I'll try to expand a bit my comment. I will assume you did a good job in your work and that the reference you would receive from who actually supervised you will be strong.

In my opinion, you can ask for two recommendation letters. One from who actually supervised you, i.e. the Research Scientist. The second, from the PI, as you feel this might help you. In the end, you formally worked for them, so it would also be strange not to have a letter from them.

I think they will gladly accept and can write a nice one even if they don't know you that well, but if you feel it's necessary you could suggest they consult with who actually followed your work, i.e. the Research Scientist, to have a better idea of your skills. I would mention this to the Research Scientist when you tell them about the letter, something like "I will also tell the PI to write one for me, but they might ask you some tip on what to write, if that's not a problem".

Good luck on the admission!

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .