It's a book about puzzles and brainteasers. There are puzzles, there are brain-teasers, there are essay-ish bits exploring some ideas in detail. There were some puzzles that I hadn't encountered before. I almost didn't see them; pretty early on the book has an essay really thinking through the problem in which someone really needs to ferry a fox, chicken, and chickenfeed across a river. I've thought plenty about that old chestnut, thank you; I was ready to put the book down. I'm glad I didn't; later on, there were plenty of puzzles I hadn't seen before, including some fun ones with numbers.