What is XP:
eXtreme Programming is a lightweight methodology (see other lightweigh methodologies here), XP is a methodology that is used to delivery software to your customers needs when its needed. XP empowers your developers to confidently respond to changing customer requirements, even late in the life cycle.XP implements a simple, yet effective way to enable groupware style development. XP is a disciplined approach to developing software. XP is successful because it stresses on customer satisfaction.
The methodology emphasizes on team work, from the developers , managers and the client. XP was intended for small project groups but there are examples of projects of 100 members that have used XP eg Though Works. The methodology is a collection of rules, each rule supporting the other rules.

The tenets of XP:
1. Simplicity
2. Communication
3. Feedback
4. Courage

Role of a developer:
One of the key tasks of a developer is refactoring ie thats a task that the client and the managers cannot enforce , only the developer/designer can do so. The programmer is also reasponsible for creating high quality code by
a) pair programming approach
b) refactoring
c) creating test cases before creating code.

XP has 4 phases :
1) Planning
2) Designing
3) Coding
4) Testing

Planning Phase:
User stories: It serves multiple purposes, it can be used instead of a requirement document , the IT integrator can use the document as an estimator and use it for release planning, the document is written by the client in non -technology terms, the client can use the document to derive the user acceptance tests. Once the big picture is created the individual developers go to the client and then get the details of the sub stories and document the same as user requirements, if a user story takes more than 3 weeks then a new story is created

XP uses iterative development process so that the project can get the agility of a change process.