Agile Principles

Agile methods are a family of development processes, not a single approach to software development. The Agile Manifesto states: We are uncovering better ways of developing software by doing it and helping others do it. Through this work we have come to value:
Individuals and interactions over processes and tools
Working software over comprehensive documentation
Customer collaboration over contract negotiation
Responding to change over following a plan
That is, while there is value in the items on the right, we value the items on the left more.

Some of the principles behind the Agile Manifesto are:

  • Customer satisfaction by rapid, continuous delivery of useful software
  • Working software is delivered frequently (days or 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
  • Daily 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

Source: Wikipidia

Contrasted with Waterfall Methodology

Agile development has little in common with the waterfall model. The Waterfall methodology is the most structured of the methods, stepping through requirements, analysis, design, coding, and testing in a strict, pre-planned, "all at once" sequence. Progress is often measured in terms of deliverable artifacts: requirement specifications, design documents, test plans, code reviews and the like.

A common criticism of the waterfall model is its inflexible division of a project into separate stages, where commitments are made early on, making it difficult to react to changes in requirements as the project executes. This means that the waterfall model is likely to be unsuitable if requirements are not well understood/defined or change in the course of the project.

Agile methods, in contrast, produce completely developed and tested features (but a very small subset of the whole) every few weeks. The emphasis is on obtaining the smallest workable piece of functionality to deliver business value early and continually improving it and/or adding further functionality throughout the life of the project. If a project being delivered under Waterfall is cancelled at any point up to the end, there is often nothing to show for it beyond a huge resources bill. With Agile, being cancelled at any point will still leave the customer with some worthwhile code that has likely already been put into live operation.