Agile Manifesto

Scrum has been used by Google since 2005. Scrum is widely used agile framework. In short Agile can be described with the following manifesto:

Individuals and interactions,over,processes and tools
Working software,over,comprehensive documentation
Customer collaboration,over,contract negotiation
Responding to change,over,following a plan
Hats off for this manifesto.

look at: for details.