What is Extreme Programming(XP)?

Extreme Programming (XP) is one of the agile methodologies which is focused on improving responsiveness to business requirement changes and software quality. It focuses on "releases" in short development cycles, improving productivity.
XP promotes pair programming focusing on extensive code reviews and unit testing. A flat management structure is another feature to cut down on bureaucracy for faster and efficient working. The basic idea is to take all relevant development steps to extreme level in order to improve overall quality of delivery whether it's development in pair, unit testing, automation of system test cases and their executions, test driven development. Acceptance testing is done and results are published and if bugs are found then test cases are written first surrounding bugs, essentially bugs are nothing but missed test cases.
XP only works on small teams of twelve or fewer people. This limitation can be overcome by breaking up project into smaller pieces and the team into smaller groups.
It promotes continuous design and release concept and can run efficiently and successfully with extremely commited senior technical worfkorce.