Some of the principles behind the Agile Manifestoz

• Customer satisfaction by rapid, continuous delivery of useful software
• Working software is delivered frequently (weeks rather than months)
• Working software is the principal measure of progress
• Even late changes in requirements are welcomed
• Close, daily cooperation between business people and developers
• Face-to-face conversation is the best form of communication (Co-location)
• Projects are built around motivated individuals, who should be trusted
• Continuous attention to technical excellence and good design
• Simplicity
• Self-organizing teams
• Regular adaptation to changing circumstances

http://en.wikipedia.org/wiki/Agile_software_development