My first interview was in their office and lasted about 45 minutes. I was interviewed by two people and all of the questions were pretty straight forward, no surprises. About a week later I had a second interview over Skype with the same 2 people as well as 2 others. This one was a lot more laid back and I could tell they wanted to get a feel for my personality more than anything. It was also helpful for me as it gave me an idea of whether or not these would be people I'd enjoy working with.