Very rigorous and well structured. 8 interviews in total (5 in first round, 3 in final round). Interviews vary between 'got what it takes' (case studies, analytics etc.) to 'want to work with' (e.g. had someone who studied philosophy interview me about everything and nothing). First round is usually done by junior employees (project leaders/ principals) and the final round is usually done by partners of the firm. Very professional, clear guidance as to what to expect (read their website www.bcg.com) during the interview process and it even includes examples of case studies you can practice before the interviews to get familiar with the concept.