There are generally three rounds of interviews once you have been selected through the written aptitude test. The first round is a case-study where a associate consultant would present you with a simple case and ask you to work on the solution for half an hour. He/she would then ask you to explain how you arrived at the answers. They might ask you a few additional questions as well. The second round is a behavioral assessment which would be taken by a consultant. The questions would mostly revolve around your previous work experience or projects you have completed at your under-graduate institution. There might be a question to guesstimate some quantity and they would ask you to walk them through your thought process. The third round is a principal interview round. This will be taken by a partners of the firm (manager/associate principal/ principal). The round would be to get to know you in brief and to assess whether you are a good fit for the team and company. All these rounds are elimination rounds with perhaps the exception of the principal interview as they would be almost certain to select you before they would send you to a partner.