Variable stars are those that change brightness. They come in many varieties, but each one provides important information about the star: its properties, its internal structure, and its evolution. This book provides a concise overview of variable stars, including a historical perspective, an introduction to stars in general, the techniques for discovering and studying variable stars, and a description of the main types of variable stars. Intended for anyone with some background knowledge of astronomy, it is especially suitable for undergraduate students and experienced amateur astronomers.