The planning game: Quickly determine the scope of the next release by combining business priorities and technical estimates. As reality overtakes the plan, update the plan. Small releases: Put a simple system into production quickly, then release new versions on a very short cycle. Metaphor: Guide all development with a simple shared story of how the whole system works. Simple design: The system should be designed as simply as possible at any given moment. Extra complexity is removed as soon as it is discovered. Testing: Programmers continually write unit tests, which must run flawlessly for development to continue. Customers write tests demonstrating that features are finished. Refactoring: Programmers restructure the system without changing its behavior to remove duplication, improve communication, simplify, or add flexibility. Pair programming: All production code is written with two programmers at one machine. Collective ownership: Anyone can change any code anywhere in the system at any time. Continuous integration: Integrate and build the system many times a day, every time a task is completed. 40-hour week: Work no more than 40 hours a week as a rule. Never work overtime a second week in a row. On-site customer: Include a real, live user on the team, available full-time to answer questions. Coding standards: Programmers write all code in accordance with rules emphasizing communication through the code.
...