You’ll need a minimum of three letters of recommendation for PhD programs and four letters for fellowships. Some applications (cough* Stanford cough) give you room for up to six letters. I’ll go over who you should consider asking for recommendations, when you should ask, and how you can prepare packets of important information that will make everyone’s lives much easier.*


Table of Contents

Who to Ask

This guide to applying to PhD programs in computer science was very helpful when I was applying and has a great section on recommendation letters. Here is a summary of the important parts.

Content matters.

  • The PhD is a research degree, so you will want someone who can attest to your skills in research. Research advisors are a great source. If you worked directly with a grad student, you can ask the PI to co-write the recommendation letter.
  • Someone who knows you well will be able to write a higher quality than someone who doesn’t. Avoid asking a professor whose class you took just because you got an A. If you have a relationship with that professor beyond just getting a good grade, then feel free to add them to the list. Also consider work supervisors, professors you TAed for, and academic advisors.

Position matters.

  • Recommendation letters will have the greatest weight when they come from people who have gone through the process and can compare you to others in a similar position. Therefore, research professors have the greatest weight.
  • Next come research scientists, lecturers, systems scientists, employers, and postdocs.
  • Bonus points for professors who are well-known in their field. Professors reading applications are more likely to trust recommendation letters from people they know.

An overview of my references, just in case it helps you.

Note: it’s hard to look for six recommendation letters—I was already stressed just looking for three, feeling like I didn’t know anyone at all. Research advisors, internship supervisors, club advisors, professors who taught you, and mentors are great people to start with when you look for LORs.

  1. Research and undergraduate thesis advisor. Well-known in NLP.
  2. Professor I TAed for. Well-known in NLP.
  3. Research advisor (for one summer). Professor who specializes in databases and data science.
  4. Dean of student life/academic advisor (supplementary)
  5. Google intern host from summer before senior year (supplementary)
  6. Instructor I TAed for from summer before junior year (supplementary)

When to Ask

You should give your recommenders at least one month to write your letters, but I suggest asking in late August/early September just to be safe. You should also send brief and friendly reminders one month, one week, three days (optional), and one day before the deadline. Alternatively, just ask your recommender if they have a reminder schedule that would help them and go with that.

How to Prepare

People have a lot going on and may not always remember all the details, so you’ll want to prepare a packet of important information to refresh their memories. On top of that, you can use these packets to ask your recommenders to highlight certain pieces of information. Some professors might prefer a paper copy, but I emailed all the files to my recommenders. Here is what should go in the packet.

Note: my advice here differs from what is stated in the guide I linked above. These are materials that I provided to my recommenders. The important part is that you provide important information in a concise, easily locatable way.

  • Summary sheet (1-2 pages) with your name, summary of key accomplishments that are relevant to that recommender, and programs/fellowships that you need letters for (plus deadlines and instructions for submitting, which is likely to be as simple as clicking a link in an automated email)
  • CV/resume You can include either. I chose to include my CV because I was already providing a shortened summary as well.
  • Personal statement (optional) One of my recommenders asked for my personal statement so I sent a draft. I didn’t send it to the rest simply because it wasn’t finished.

Don’t forget a thank you note!

When application season is over, you have your results, and you have made your decision, don’t forget to send a thank you message to each of your recommendation letter writers. Writing letters is hard work and I’m sure they would be curious about what you end up doing! You don’t even have to wait all the way until the spring—saying thank you more than once doesn’t hurt. :)