Two rounds - first round included 2 interviews, both had 15 minutes of a fit interview and 30 minutes of a case interview. The cases themselves were straightforward. The interviewers at BCG are very friendly. I didn't make it to round 2, unfortunately. I was told that I needed to be more creative with the use of frameworks. Didn't seem like a hard interview, but I guess they were expecting more in terms of how I approached the case.