A concise but thorough introduction to the observational data and theoretical concepts underlying modern astronomy, "Astrophysics in a Nutshell" is designed for advanced undergraduate science majors taking a one-semester course. This well-balanced and up-to-date textbook covers the essentials of modern astrophysics - from stars to cosmology - emphasizing the common, familiar physical principles that govern astronomical phenomena, and the interplay between theory and observation. In addition to traditional topics such as stellar remnants, galaxies, and the interstellar medium, "Astrophysics in a Nutshell" introduces subjects at the forefront of modern research, including black holes, dark matter, gravitational lensing, and dark energy, all updated with some of the latest observational results. To aid physical understanding, mathematical derivations are kept as simple, short, and clear as possible, and order-of-magnitude estimates, dimensional analysis, and scaling arguments are frequently used. These no-nonsense, 'back-of-the-envelope' calculations train students to think like physicists. The book is amply illustrated with simple, clear figures and each chapter ends with a set of problems. In addition to serving as a course textbook, "Astrophysics in a Nutshell" is an ideal review for a qualifying exam and a handy reference for teachers and researchers. This is the most concise and up-to-date astrophysics textbook for science majors. It contains a broad and well-balanced choice of traditional subjects and current research topics. It uses simple, short, and clear derivations of physical results. It trains students in the essential skills of order-of-magnitude analysis. It includes teaching problems with each chapter.