Lots are jokes. Organization is poor, as the book starts by tricking the reader unfairly, and only later teaches about the different kinds of riddles. Worth reading if you find a copy handy, as I did in a Little Free Library, but not worth buying. Btw, I was surprised to see the extensive notes and bibliography... like a scholarly book!
Notes: awesome brainteaser book loaded with riddles that are smart -- not joke-type riddles the only problem is the solutions are too easy to "accidentally" look at