First round: two back-to-back 30 minute interviews on campus. A mix of behavioral and "case" questions. I received word later that evening that I'd move on to the second round interviews the next day. Second round: two additional back-to-back 30-45 minute interviews on campus. Not significantly more detailed or difficult than the previous day's interviews, but with slightly more senior interviewers. The "case" questions were much less involved/less structured than a consulting case interview, but still required carefully thinking through certain business scenarios in Amazon's retail business, describing all of the elements I would want to consider, thinking about what sort of data I'd need, and how I'd reach a decision. Amazon is very interested in creating the best consumer experience and making data-driven decisions, so keep those points in mind throughout the interviews.