As one of the authors of the Agile Manifesto, Dave Thomas understands agility. As the author of Programming Ruby, he understands Ruby and how to describe writing Ruby applications. David Heinemeier Hansson is the creator of the Rails framework. Leon Breedt wrote the web services component of Rails. Mike Clark is an international Rails trainer and an expert on testing techniques. James Duncan Davidson manages a number of Rails applications and talks about Rails deployment around the world. Justin Gehtland trains developers on AJAX, Web 2.0, and Rails. Andreas Schwarz wrote the online Rails security Manual. The authors know Ruby, and they know Rails.