How do cells convert simple nutrients to living biomass? The simple answer is through a series of controlled chemical reactions called metabolism. But what are these chemical reactions, how are they controlled, and how are they arranged into a metabolic network that assembles complex cells while obeying the rules of chemistry and physics? In this brief introduction, we explore enzymes (structure, kinetics, and regulation), bioenergetic principles of reaction coupling and redox reactions, and give a taste of metabolic pathways and regulation. The book is designed for students with a minimal background in chemistry.