These modules introduce students (and anyone else who's interested) to the mathematical underpinnings of what they learn in introductory biology courses. But unlike a textbook, the modules are not full of equations and proofs. Instead, we try to bring math to life using intuitive approaches, everyday situations, and even humor. The modules contain hundreds of interactive activities, games, and questions. They range from the relatively simple (what to do with division) to the relatively abstruse (discrete diffusion models).