We connected with an undergrad in the lab who was planning to apply for several summer research programs. They wanted to know how many recommendation letters they could ask each professor to write. As usual, we edited the conversation for brevity and to remove identifying details so the student remains anonymous.

Hi! I'm an undergraduate student...applying for REUs for the first time! Many of the projects interest me and I'd love to apply to as many as possible... I've researched under two professors for the past couple of years and thought they would be the best professors to write my letters of recommendation. I was wondering how many projects it is appropriate to ask the same professor to write my letters of recommendation for? Thank you so much for your help!

Dear Undergrad In The Lab,

Your instincts about asking your research professors to write recommendation letters for a summer research program is spot on.

As far as how many letters each professor will be willing to write for your applications, well, that’s a little more complicated. The number is basically professor-dependent. While one professor might happily write 5 letters another might prefer to write only 1 or 2. Because this letter probably won't need to be customized for each program, some professors will be wiling to send 10 or more letters but others might decline such a request.

Fortunately, you won't need to guess how many letters your professors will write because you'll ask them. When asking, use a phrase similar to: “I’m applying to [X] summer research programs. Will you be able to write strong letters for me?”

But before you decide on the what number stands in for X, read on.

I recommend that you reconsider applying to “as many [programs] as possible” and instead focus on ones that are the most interesting to you science-wise and ones where the expectations for undergrads in the program are compatible with how you wish to spend your summer.

Although many summer programs have similarities, it’s often their differences that make a happy and productive summer or an unfulfilling or miserable one. These differences aren’t about the programs so much as about how you, as the student participant, feels about the expectations of how you'll use your time and type of research you'll be doing.

Every summer we receive DMs from undergrads who regret the summer program they chose. The reasons for their unhappiness vary but many selected programs without carefully reading (or ignoring) the expectations for undergrads before applying, or chose research they weren’t genuinely interested in because they thought it wouldn’t matter. (There are other reasons for unhappy summer research experiences too but those aren't relevant to this post.)

Frustrated students have regretfully told us, “I didn’t realize that 40 hrs a week in the lab meant I had to work the whole time,” and “I’m basically doing the same techniques and project I did during the semester only it’s more boring because it’s all day everyday,” and “I chose this because it’s in [location] and paid a lot but I don’t care about [the lab’s big picture] because it’s not relevant to anything I want to do in the future.” In most of these cases, the student would probably have been happier in a different program or perhaps spending their summer pursuing other goals instead of undergrad research.

But from our conversation, it's clear that you're excited to spend your summer in a full-time research experience. And because there are numerous summer programs that interest you, and landing a spot is competitive, applying to multiple programs is a good strategy. But I can't definitely say what the magic number of programs for you will be. When I've asked undergrads (and former undergrads) to weigh in on how many summer programs they applied to it ranges from as low as 1 to as many as 20. This is a good discussion to have with a mentor who knows you well--perhaps a labmate or the professors who you plan to ask to write letters for you.

Once you’ve selected the programs you want to apply for, connect with each professor to ask for letters. They might be willing to write all the letters you need or they might set a lower limit. If the latter happens, you might choose to apply to only your top-ranked programs or search for additional letter writers and apply to all.

Further reading:
Help your professors and mentors write the strongest recommendation letter possible. Use the tips in One Letter to Rule Them All to get started.