Agile Manifesto
We are uncovering better ways of developing software by doing it and helping others do it. these are our values and principles.
http://www.agilemanifesto.org/
Best coding practices
Extreme programming explained
http://www.bestcodingpractices.com/extreme_programming-45.html
Gentle introduction to XP
Extreme programming: a gentle introduction
http://www.extremeprogramming.org/
XP glossary
XP glossary
http://www.diamond-sky.com/resources/xp/glossary.html