Several interviews. A 1 hour long HR screen (only time I've ever seen that) followed by hiring manager, technical interviews, and at least one executive interview. The HR person described their interview process as very difficult and lengthy. I can't remember exactly but I believe they said 6 interviews in total.

I interviewed with 2 of the development staff. They discussed the business and their process. They then asked me about my experience in each aspect of the projects. They talked about how they are more of consultant firm and how they deal directly with clients. Pretty straight forward and pleasant experience.