Jim Highsmith was one of the original authors of the Agile Manifesto (see previous post), and is recognised as being one of the leading practitioners and thinkers in the field of agile project management operating in the world today. He suggests that software development is a moving target, and for project management methodologies to be successful, they need to be adaptive - very much the way we see agile project management methodology.
Jim released a book - Agile Project Management - in 2004, in which he sets out his theories and practical advice on how to run agile projects. You can read more about Jim at his website - www.jimhighsmith.com.