Story: Substance, Structure, Style, and the Principles of Screenwriting
By Robert McKee
Yes, this is a screenwriting book. However, we've found it to be one of the most comprehensive books written on storytelling (which is absolutely crucial to the Dad's style of improv). Story is a great resource for learning the ins and outs of scene structure, character arcs, and genre. This should be especially of interest to those of you interested in long form improv.