The extragalactic universe, the immense world of a billion galaxies lying beyond out own, is the subject of this book. Our Sun is but a tiny star among a hundred billion other in our Galaxy, the Milky Way, which appears as a luminous veil trailing across the clear night sky. Beyond the Milky Way we will soar into space amid galaxies, clusters of galaxies, radio galaxies and quasars of enormous energy, out to the cosmological horizon which arrests our flight like an intangible barrier. Why do galaxies seem to fly from us? Is space so strongly curved that by going straight ahead we come up behind ourselves? Did it all begin with an enormous explosion, the famous Big Bang, which decided our fate in the first quarter of an hour? These are the questions which this rigourous and enthusiastic scientist tries to answer with complete honesty and non-technical clarity.