Applied through my university and was brought in for first-round interviews at the local (Boston in my case) office. Interviews were 45 minutes long, back-to-back: 10 minutes for fit questions, 30 minutes for case interview, 5 minutes for Q&A. Was flown to the Chicago office (my eventual home office) for second-round interviews, which were structured a little differently: 1 verbal case, like in the first round, and one hour and a half written case + presentation. Met many different BCGers along the way and was impressed with how frank and honest they are through the entire process!