Just finished the book Project Management with Scrum, and it is excellent.
Here a great overview quote from the forward:
"Gary Convis notes that Toyota's sustainable success comes from an 'inter-locking set of three underlying elements: the philosophical underpinnings, the managerial culture an the technical tools. The philosophical underpinnings include a joint [worker] , customer first focus, an emphasis on people first, a commitment to continuous improvement...The managerial culture...is rooted in several factors, including developing and sustaining a sense of trust, a commitment to involving those affected by first, teamwork, equal and fair treatment for all, an finally, fact-based decision making and long-term thinking.'
Scrum works for all the same reasons. Its philosophical underpinnings focus on empowering the development team and satisfying customers. Its managerial culture is rooted in helping others achieve their goals. Its technical tools are focused on making fact-based decisions through a learning process. When all of the factors are in place, it's hard for Scrum not to succeed. - Mary Poppendieck"
From Agile Project Management with Scrum (Microsoft Professional).