First, they schedule a phone interview that involves a 30-minute case and a 30-minute behavioral interview. The case is done over phone and webex - it's generally pretty easy. If you pass that, you move onto the final interviews, which take place at a ZS office. This portion consists of two cases (with managers), behavioral interview (with a principal), lunch (with associate or associate consultant), and a demo (with associate or associate consultant). They really try to gauge if you are a good "fit", so try to be personable during the lunch and demos (ask questions, be engaged, etc.), and obviously try your best on the case - you have to really bomb it to not get an offer.