Check out the above video. It’s an interview with Mike Cohn (about 10 minutes long). In this interview, Mike talks about scaling agile across the enterprise, on projects as large as 700 people!
Mike is the author of the popular books, Agile Estimating & Planning and User Stories Applied. Personally I particularly like the User Stories Applied book. I’ve written quite a few blog posts about Writing Good User Stories. They are so simple, yet so empowering.