Textbook for the language LISP by Daniel P. Friedman and Matthias Felleisen. The Little LISPer seems unique in its approach to computer science instruction: the entire 200+ page book (and even the review on the back) are a series of questions and answers, with questions on the left side of every page and answers on the right.

from the book:

Is it true that this is an atom?
atom

Yes,
because atom is a string of characters beginning with the letter a.

I find this to be a tremendously refreshing way to learn a programming language, and wish there were more textbooks that took a non-traditional approach like this.