Providing a comprehensive and up-to-date treatment of observational cosmology, this advanced undergraduate textbook enables students to use quantitative physical methods to understand the Universe. The textbook covers recent developments such as precision cosmology and the concordance cosmological model, inflation, gravitational lensing, the extragalactic far-infrared and X-ray backgrounds, downsizing and baryon wiggles. It also explores the future missions and facilities likely to dominate cosmological research in the future, including radio, X-ray, submillimetre-wave and gravitational wave astronomy. Each chapter contains full-colour figures, worked examples and exercises with complete solutions. Clearly identified key facts and equations help students easily locate important information. Suggestions for further reading provide jumping-off points for students aiming to further their studies. Reflecting decades of Open University experience in undergraduate teaching, this textbook brings students to the forefront of the rapidly developing field of observational cosmology. Accompanying resources to this textbook are available at: http://www.cambridge.org/features/astrophysics.