Does fine-tuning support the existence of a multiverse?

In the context of the probabilistic fine-tuning argument for the existence of a divine designer, appeals to the existence of a multiverse have often seemed ad hoc. The situation is rather different though if there is independent evidence from physics for a multiverse. This paper argues that the fate of the fine-tuning argument depends on open questions in fundamental physics and cosmology. It also argues that the many-worlds interpretation of quantum mechanics opens up new routes to undercutting the force of the fine-tuning argument.