One phone interview that seemed fairly scripted, and a second Skype interview with more personalized questions and that addressed the specific openings I was interested in. The interview is relatively easy to prepare for, but be aware that initially you are applying to all available fellowships and may not be offered your first choice.

Three rounds of interviews. First a pretty standard call with with HR from SEI. After that, I had two more interviews with my potential site manager. Although I've also read that some people have had only one and some people have had three or more with site personnel. All were fairly standard and the process was pleasant.