There are Four core values for XP
1. Communication
The more you communicate, the less you make a mistake
2. Simplicity
The simpler the system is, the less you have to communicate
3. Feedback
a. Feedback from tests
b. Feedback from people
The more feedback you have,the less risky it will be
4. Courage
It is the courage to make a overall change, or to throw away code.
And there is a deeper value: Respect between each other. "If members of a team don’t care about each other and what they are doing, XP is doomed."