Friendly and professional from start to finish, very well organized. Started with phone screen and then a discussion of what to expect going forward. HR contacted me just before my first face-to-face interview to check on how I was doing and if I had any last minute questions. After that, I moved through 3x interview days, each one consisting of back to back 1-hr interviews with 2x BCG employees, with increasing seniority. It was almost exactly as described online, some personality/behavioral questions, followed by a case interview and then time for you to ask them some questions. The case interview is often a project that the interviewer themselves worked on, so you cannot predict what it will be like; it pays to study the cases on BCG's website as well as practising case interview techniques in general.