Two phone interviews: one was a mix of behavioral and technical, the other purely technical. Each lasted about 45 minutes. Then, the on-site interview onslaught you may have heard before: they flew me down to LA and put me up in an awesome suite in Redondo Beach, and had me come to the Hawthorne headquarters at 9 am one morning. The interview is in two segments, a presentation and a number of one-on-ones. I gave a fifteen-minute slideshow and talk about a project I'd worked on for school to four engineers and a hiring manager, then fielded questions from them about a number of different aspects of the project. Things like what I could have done differently under different constraints, math behind some of my finished work, etc. This went on for about half an hour, and also touched on some of my past internship experiences. After the presentation and questioning, I was directed to wait in a separate conference room while they deliberated about me. At that point I was pretty nervous because some applicants are dismissed there, but after about ten minutes one of the engineers came in and assured me that things were going well. He and I believe three others took turns interviewing me one-on-one for about 25 minutes each. I asked and answered all kinds of questions, ranging from thermodynamics concepts and general things about the team to large consulting-type problems. Finally (this was around noon), I had lunch with a few members of the team before leaving. Two and a half weeks later, I received an offer from the hiring manager.