This text is an overview of modern cosmology, written at a suitable level for undergraduates. It introduces the main constituents of the universe, and the methods most commonly used to study them. It then discusses some of the latest ideas and theories in modern cosmology, including studies of active galaxies and IRAS galaxies, the discovery of the cosmic microwave background radiation and its impact on the Big Bang Theory, and the latest thinking on the age and size of the universe. Worked calculations are included throughout the book, and diagrams plus mono and colour photographs illustrate important aspects of the text.