I heart Michael Gellman. Aside from giving me the single most effective side-coaching I think I've ever received (Example: "BULLSHIT!"), he's genuinely giving as a teacher and an audience member (I remember very clearly hearing him "ooooooh" a game-move I made at the AND Performance Improv Retreat—and I thought, "BINGO, I've figured this scene out.") So I couldn't wait for his book, Process: An Improviser's Journey.
It's a narrative, modeled after An Actor Prepares (which is on my shelf...and on the list). Because it's about a student going through his workshop, you get a real sense of the exercises, the notes and what goes on in your head when you succeed or fail. His teaching style is very organic—"process" is the perfect title.
It's rare that a book can bring experiential learning to life. This one totally captured the feeling of studying with him. Man, I liked it an awful lot.
Staying in the same mode, I cracked into Kenn Adams' How to Improvise a Full-Length Play: The Art of Spontaneous Theater. It's a completely different approach—very structured, very linear. It's a tougher read—more text-book-y—but I'm digging it in a completely different way. More to come when I hit the end...maybe a side by side comparison.