Improvisation Instruction at its best
This is the best improvisation book I have come across because it actually has instruction and rules about improvisation. It's not just a list of improv situations and games - it's a real "how-to" and "why" and "what appeals to an audience" book. I teach improvisation and even though other books are great resources, this one is a front runner just because of its instruction aspect of the whole concept of Improvisation.