Best Practices for Agile/Lean Documentation
http://www.agilemodeling.com/essays/agileDocumentationBestPractices.htm

Ambler, Scott W.
Agile Modeling
2001

Abstract:

Documentation is an important part of agile software development projects, but unlike traditionalists who often see documentation as a risk reduction strategy, agilists typically see documentation as a strategy which increases overall project risk and therefore strive to be as efficient as possible when it comes to documentation. Agilists write documentation when that's the best way to achieve the relevant goals, but there often proves to be better ways to achieve those goals than writing static documentation. This article summarizes common "best practices" which agilists have adopted with respect to documentation.