Learning math ought to be joyous, like playing musical instruments or sports. It’s fun to figure things out! Calculus can be particularly fun because it helps so many different problems so simply. Unfortunately, the way most schools teach calculus is horrid. Too much focus on terminology and rules, not enough on comfort with the concepts. Too much memorization, not enough inspiration. This book takes a revolutionary approach, focused on play. The 150 pages of text are colorfully illustrated and spiced with over 70 interactive widgets and hundreds of solved problems. They motivate core calculus concepts, explain them intuitively, provide simple proofs of major results, and apply them to better understand our wondrous world. Use it as your core textbook or to liven up duller ones.