I began the interview process as a referral in December and set up a first round phone interview for early January. I flew out a couple weeks later for an on site super day. The recruiter was nice and very helpful even though we were working together around the holidays. First Round: Case Interview (30 Minutes - Phone): The case wasn't too challenging but you are forced to make recommendations on the spot and run calculations which can be stressful. Try to sound confident and be articulate. Behavioral Interview (30 Minutes - Phone): Three standard fit questions followed by my own questions for the interviewer. I was invited to a second round at the San Mateo office. There were three interviews, a project demo, and lunch with a current Business Associate. Second Round: Lunch: Very casual, make sure you show interest in the company and be personable. Behavioral (30 Minutes): Mine was with a principle, not very high stress. Three fit questions, each of which turned into a small conversation. See above. Analytical Case (80 Minutes): You are given 40 minutes of prep time to work through a packet of information, make calculations and recommendations, then draw up a few ppt slides to walk through with a consultant. This was the most stressful part of the day. You'll be rushed so make sure you double check you numbers, ZS really cares about quant skills. Project Demo (45 Minutes): A Business Associate went over a few quantitative and qualitative projects typical of a BA. Make sure you show interest and ask good questions. Case Interview (45 Minutes): Very similar to the first round case interview only in person. Overall great experience. I was stressed but confident enough not to let it show. Double check all of your calculations and try to be articulate. They emphasized multiple times that they're looking for someone who not only can do the job well but also fit in the culture. I felt like I fit in well which made me less anxious overall. People: It's a very young office with people from all over the country. Everyone that I met was very intelligent and seemed like they enjoyed their job.