I had an incredible experience being interviewed at Amazon! What impressed me the most was, despite being such a big company, the process was extremely agile and the people I had contact with were extremely nice. First I had a phone interview and after that I was invited for 4 interviews in a row, in their offices in London. I was also challenged to perform a numerical reasoning test online. The interviews go according to a specific method (STAR - situation, task, action, results) and are based on their 14 Leadership Principles. My advice is to study a lot and prepare the principles as well. You will find a lot of frequently asked questions for each principle in the internet and Amazon itself provides a lot of information and tips for you to get prepared!