Agile development emphasizes close collaboration between the programmer team and business experts; face-to-face communication (as more efficient than written documentation); frequent delivery of new deployable business value; tight, self-organizing teams; and ways to craft the code and the team such that the inevitable requirements churn was not a crisis.
It helps the companies to adopt proactively to ever changing requirements. They are revolutionary in the sense that they contradict the tradional waterfall model in many ways and present a whole new different yet very practical approach to software development process.
Read the Manifesto for Agile Software Development at: http://www.agilemanifesto.org/
and visit the agile alliance at http://agilealliance.org/ to get more info about agile methods.