As we discussed in the Introduction, Badiou calls for a contemporary atheism, an atheism that breaks with the three Gods that continue to hold thought captive: the God of religion, the God of metaphysics and the God of the poem. Since the influence of these gods ultimately rests on the persistence of the theme of finitude, we must take leave of the latter as the horizon of philosophical speculation. Put more positively, we must unseal the infinite from the one, restoring it to the banal multiplicity that it is. This chapter discusses Badiou's attempt to unbind the infinite from its collusion with the one, by discussing the main elements of Badiou's ontology. However, to be clear, no attempt will be made to provide a copious overview of Badiou's ontology in its entirety, examining all the twists and turns involved in its complex presentation. There are already numerous good introductions to Badiou's ontology and critical discussions of its particular elements already in print, and there is no need to repeat the work of others on these issues. Rather, in keeping with the focus of this book, the goal of this chapter is to read Badiou's ontology and its main themes as an anti-theology, an anti-theology that takes its departure from the main thesis of Being and Event: “mathematics is ontology” (BE 4, original emphasis).