Useful online sources about theatre improvisation
ImproWiki.com. The name says everything… very very rich!
Books and Authors
Keith Johstone “Impro” and “story telling”. These are the bybles of theatre improvisation, mainly the first one.
Viola Spolin and her games. She wrote the first handbook of theatre improvisation with plenty of games with accurate explanation. Maybe today it is a bit outdated, nevertheless this is a great source for coachings.
Omar Galvan with his improtour. He wrote an excellent handbook for Castillan- and Italian-readers, and here his speech for TEDx.