One of the first Agile software development methods, which emphasizes excellence of development skills over complex project management.
In XP, twelve technical practices based on the values of communication, simplicity, feedback and courage structure short iterations focused on the delivery of high-quality products. The customer is highly involved in the definition and prioritization of the functionalities (story cards) to be developed, while the small (12 people or less) self directed and closely integrated development team uses continuous testing and planning, and short feedback loops to deliver shippable software at very short intervals (1 to 4 weeks).
see also: agile methodology, scrum, feature driven development, dynamic systems development method, crystal methodologies, lean software development