A groundbreaking approach to mathematical pedagogy, WhoIsFourier is an enormously popular exposition of FourierAnalysis written by and for 8-year-olds. But educators and undergraduates can learn a lot here too. Taking seriously the proposition that math is a language, the Japanese "Hippo" schools have taught the subject as a language complete with songs and games. This book is proof that most Western math books are not merely boring, but actively destructive to the faculty of mathematical curiosity.
Real cute.