Agile is a way to manage projects. It can be used for virtually anything, but it was founded in software development. This handbook focuses on agile for software development, but many of the principles can be expanded to other fields. Agile breaks down larger projects into small, manageable chunks called iterations. At the end of each iteration (which generally takes place over a consistent time interval) something of value is produced. The product produced during each iteration should be able to be put into the world to gain feedback from users or stakeholders. Unlike Waterfall project management, which is strictly sequenced: you don’t start design until research is done and you don’t start development until the designs are signed off on; agile has designers, developers and business people working together simultaneously.

As made popular by the “Agile Manifesto”, agile values:

  • Individuals and interactions over processes and tools
  • Working software over comprehensive documentation

  • Customer collaboration over contract negotiation

  • Responding to change over following a plan

Agile realizes that software (and marketing) projects are inherently unpredictable. Over the course of any project there are likely to be changes. Be it market changes or feature changes as the product comes to life. Agile embraces this unpredictability. By breaking down projects into small chunks, it makes it easy to prioritize and add or drop features mid project. Something that is impossible in traditional waterfall projects.

Source: http://agilehandbook.com/agile-handbook.pdf