They came to my school for an initial interview. Later I had 4 interviews with different managers and employees. It was the most difficult interview I have had. They asked me things that nobody else had asked (even Google and Apple). I turned down Apple for Groupon because I knew that I would have more say and would be exposed to more of the company, not pigeonholed in one tiny part of the business. The interview process was very rigorous and they take hiring pretty seriously.