The author – a leading theoretical cosmologist – expands on his widely acclaimed lecture notes in this self-contained textbook, suitable for the advanced undergraduate or starting graduate level.Presenting the key theoretical foundations of cosmology and describing the observations that have turned the subject into a precision science, the author keeps the student in mind on every page by explaining concepts step-by-step, in an approachable manner.After describing the dynamics of the homogeneous universe, the book traces the evolution of small density fluctuations, which were created quantum-mechanically during inflation and are today observed in the cosmic microwave background and the large-scale structure of the universe.The book is ideally suited as a course companion or for self-study.With all necessary background material covered, students have everything they need to establish an unrivalled understanding of the subject.Complete with many worked examples, figures, and homework problems, this textbook is a definitive resource for advanced students in physics, astronomy and applied mathematics.