This volume presents an unique and accessible synthesis of modern cosmology. In recent years, observational cosmology has made remarkable advances, bringing into sharper focus a new set of fundamental questions that Martin 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.