This volume presents a unique and accessible synthesis of our understanding of modern cosmology, written by one of the world's foremost contemporary cosmologists. In recent years, observational cosmology has made remarkable advances, bringing into sharper focus a new set of fundamental questions that Professor Rees addresses in this book. Why is the universe expanding the way it is? What were the 'seeds' that caused galaxies, clusters and superclusters to form? What is the nature of 'dark matter'? What happened in the very early universe? The latest exciting advances and theories are discussed, while maintaining a clear distinction between aspects that now have a firm empirical basis and those that remain speculative. Its wide scope and clear writing will be welcomed by anyone interested in cosmology and extragalactic astrophysics who has a basic grounding in physics, as well as academic researchers and graduate students in the field.