Not to be confused with the "Fairness" Doctrine (which, in a way, is its polar opposite), the "Fair Use" Doctrine is a federal law which outlines the rules under which one is allowed to reproduce, without permission, copyrighted materials belonging to another.
My understanding is that all of the principles that make up the doctrine first developed through the common law and was then codified into law: http://en.wikipedia.org/wiki/Fair_use_doctrine .
