Jamey Aebersold is the classic jazz play-along improvisation primer. I found it a great start, especially the play-along exercises. Even better when used along with the Yamaha Silent Brass system. Perfect for the those late-nioght jam sessions when you don't have anyone to jam with and don't want to wake up the neighborhood. My only point of criticism is that the introduction and instructions are rather dense - it takes a bit of work to get into the book and get started with the playing. However, it isn't necessary to master all the theory before tackling the play-along exercises. All in all, a most useful accessory for the trumpet player who wants to learn jazz improvisation.