Extreme Programming (XP) defines a process for developing
software: it addresses the problem from early exploration to delivery.

We’ll explore XP from the inside to the outside.
First, XP is a programming discipline. We’ll look at a core innovation:
how “test-first” changes the programming process itself.
We’ll also discuss refactoring, the way XP programmers improve
their code.
Second, XP is a team discipline. It has evolved a number of
practices that help produce a high-performing team. We’ll compare
XP to alternative practices, and see some of them in action.
Finally, XP is a discipline for working with customers. XP has
specific processes for planning and daily activity. We’ll see how a
team might schedule a release or iteration, and what the team
does all day.