This book considers recent claims that our universe is 'fine tuned for producing Life'. For instance, that if its early expansion speed had been smaller by one part in a million then it would have recollapsed rapidly; that with an equivalently tiny speed increase, no galaxies would have formed; and that either way, this universe would have been lifeless. Many cosmologically important numbers can seem to show similar tuning. Did God choose them with immense care? Alternatively, may there exist a great many universes, huge cosmic domains very varied in their properties? Living beings would then observe only the (perhaps very rare) universes with life-permitting properties. Universes discusses the alleged evidence of fine tuning; mechanisms by which a very varied set of universes might be generated; various forms of Anthropic Principle; and whether belief in God could be preferable to accepting the universes in vast numbers.