 Philosophical debates in which “fine-tuning” appears are often about the universe’s fine-tuning for life: according to many physicists, the fact that the universe is able to support life depends delicately on various of its fundamental characteristics, notably on the form of the laws of nature, on the values of some constants of nature, and on aspects of the universe’s conditions in its very early stages. Various reactions to the universe’s fine-tuning for life have been proposed: that it is a lucky coincidence which we have to accept as a primitive given; that it will be avoided by future best theories of fundamental physics; that the universe was created by some divine designer who established life-friendly conditions; and that fine-tuning for life indicates the existence of multiple other universes with conditions very different from those in our own universe. Sections 1–4 of the present article review the case for this fine-tuning for life, the reactions to it, and major criticisms of these reactions. Section 5 turns from fine-tuning for life to the criterion of naturalness—a condition of no fine-tuning in a rather different sense which applies to theories in quantum field theory and plays a large role in contemporary particle physics and cosmology.