Iterative Development

• Iteration: 1-4 week period in which anaylisis, design, coding, and testing phases occur, and the output is a working portion of your program.
• Rapid feedback: rather than waiting six months, the team gets feedback early and often.
• Business steering: the project sponsor has frequent opportunities to change direction and clarify requirements.
• Improved estimates: measuring the output produced in each iteration allows for increasingly accurate estimates.

To customers and managers, Extreme Programming promises that they will get the most out of every programming week. Every few weeks they will be able to see concrete progress on goals they care about. They will be able to change the direction of the project in the middle of development without incurring exorbitant costs.

Kent Beck