This textbook for graduate students in observational astronomy, describes the methods used to measure the radiation (mostly in the optical domain) from stars. It starts with an overview, followed by definitions of the main terms encountered in the subject. This is followed by a description of the fundamental physical theory of the measurement of radiative flux. Wide ranging problems in astronomical photometry are then approached. The central chapters deal with photometer design, data handling techniques, and the generation of light curves. Many applications of photometry are then described. Users of this textbook will be able to develop an interest in the practicalities of obtaining data of good quality from photometry. The book will appeal to amateur and professional astronomers engaged in variable star observations and the measurement of stellar luminosity. It is intended to encourage interest in the practicalities of observational astronomy and an understanding of stellar astrophysics from a data-based perspective. It fills a gap between a popular approach and a research monograph.