In this Very Short Introduction, popular science writer John Gribbin tells the story of our growing understanding of galaxies, from the days before Galileo to our present-day observations of our many hundreds of millions of galactic neighbors. Their study has revealed much of what we know today about the cosmos, providing a window on the Big Bang and the origins of the Universe. He looks at our own "Milky Way" Galaxy in detail, from the different kinds of stars that are born within it, to the origins of its magnificent spiral structure. Gribbin describes the many discoveries that have been made about our own galaxy and those beyond: how a super massive black hole lurks at the center of every galaxy, how enormous forces are released when galaxies collide, how distant galaxies provide a window on the early Universe, and how the formation of young galaxies shed needed light on the mysteries of Cold Dark Matter.