It was informal. I reached out to the professor, rather than university. We had some preliminary phone calls and email exchanges. I traveled to Boston to give a presentation and was given the position. My travel was reimbursed.

The interview consists of several parts. First was a phone interview. The potential PI called me and briefly introduced herself to me. Second, it was a on-site interview. I gave a presentation and had a lunch with group members. In the afternoon, I had a talk with the program chairman, she asked me about my passion and interest, as well as introduction of the program and the format of training I would get in the next 2 years.