eXtreme Programming
eXtreme Programming (XP), developed primarily by Kent Beck, is a software development discipline built on the values of simplicity, communication, feedback, courage, and respect. One of the first agile methods, it popularized pair programming, test-driven development, continuous integration, refactoring, and sustainable pace.
Key Principles
Beck, Kent; Andres, Cynthia. Extreme Programming Explained: Embrace Change, 2nd Edition, Chapter 5.
Fourteen principles: Humanity, Economics, Mutual Benefit, Self-Similarity, Improvement, Diversity, Reflection, Flow, Opportunity, Redundancy, Failure, Quality, Baby Steps, Accepted Responsibility.