E-mail correspondence to set up an initial interview with an HR rep, just your basic screening interview to ensure that I knew what the job was and did indeed meet at least the minimum qualifications.
Same HR rep set up a phone interview between one of the on-site managers and I. That interview was more basic questions about my qualification and the a lot of chatting about the company in general. The on-site interview, also set up by the same HR rep, was a set of several (5-6) one-on-one interviews with on-site managers and lead engineer types. The questions were almost entirely behavioral style and were fairly easy.
The whole process was pretty enjoyable, and all the people were amicable. However I will say this, after the on-site interview they kind of just ignored me and never got back to me again. I was at least expecting a "Thanks but no thanks" e-mail in response. I'm one of those people that considers it ineffably rude to not get back to candidates you took the time to interview on site.
Overall, it was a decent experience and I do like the company.