Now in paperback, this book is the first comprehensive and coherent introduction to the role of cosmic strings and other topological defects in the universe. This study has been one of the major driving forces in cosmology over the last decade, and lies at the fruitful intersection of particle physics and cosmology. After an introduction to standard cosmological theory and the theory of phase transitions in the early universe, the book then describes, in turn, the properties, formation, and cosmological implications of cosmic strings, monopoles, domain walls and textures. The book concludes with a chapter considering the role of topological defects in inflationary universe models. Ample introductory material is included to make the book accessible to the wide audience of particle physicists, astrophysicists and cosmologists for whom this topic is of immediate interest.