What is
Extreme Programming (XP) is an agile software development framework that aims to produce higher quality software, and higher quality of life for the development team. XP is the most specific of the agile frameworks regarding appropriate engineering practices for software development.
How to
It advocates frequent releases in short development cycles, intended to improve productivity and introduce checkpoints at which new customer requirements can be adopted.
Other elements of extreme programming include: programming in pairs or doing extensive code review, unit testing of all code, not programming features until they are actually needed, a flat management structure, code simplicity and clarity, expecting changes in the customer’s requirements as time passes and the problem is better understood, and frequent communication with the customer and among programmers.
Take everything to the extreme! For example, take code review to the extreme lead to pair programming.