In 1993, Professor Rees was invited by the Accademia Nazionale dei Lincei to give a series of lectures reviewing the progress of cosmology and its future prospects. Based on those lectures, this volume presents a unique synthesis of our understanding of modern cosmology. Observational cosmology has made remarkable advances in recent years, and has brought 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 grow? What is the nature of 'dark matter'? Many key issues and current controversies are also considered, but throughout a clear distinction is maintained between aspects that now have a firm empirical basis, and those that remain speculative. Given the unique contribution Professor Rees has made to cosmology, this book will be welcomed both by researchers in the field, and beginning graduate students with a background in physics.