Round 0: telephone interview. General questions: why BCG, why management consulting etc.
After that, the case interviews start. I read most of the preparation available across the internet, but all my cases were impossible to prepare for. You will have to be creative to find a useful framework once the problem is presented to you.
Round 1:
A) computer test. Case-like number questions with multiple choice answers (+- 1h)
B) Case interview + general questions with a project leader (+-1h)
Got feedback the next day. Useful stuff to improve for your next round. You are also assigned a "buddy": someone at BCG you can ask any question you'd like but who does not interfere at all with your application procedure. Great system.
Round 2:
A) In basket case with a principal: around 30-40 pages with text, quotes, graphs, numbers etc. to solve 3 case-like questions. You get 2 hours to prepare some slides to answer these questions. This is followed by a 1h interview where you have to explain your reasoning. Also, the same general questions.
B) Case interview + general questions with a principal (+- 1h)
This is where your stamina is tested because it's right after the in basket case
Got feedback after 2 days. Again useful stuff to improve for your last round.
Round 3:
A) Case interview + general questions with a project leader (+- 1h)
B) Case interview + general questions with a sr. partner (+-45 mins)
Got feedback the next day. Did not get an offer but they didn't really explain where I dropped the ball. Sr. partner was 20 minutes late, disinterested from the start and kept using his phone during the interview. Left me with a sour feeling after a generally very positive experience.