On many influential definitions of mental health, mental health is intimately connected to, or even identical with, well-being. What can theories of well-being tell us about mental health, and what can considerations of mental health tell us about theories of well-being? I outline the various relationships between the main theories of well-being and the main theories of mental health, and argue that we are left with a choice between two broad views. On the first view, mental health is partially constitutive of well-being, mental health is importantly different from bodily health, and a surprisingly large number of possible conditions count as mental health problems. On the second view, mental health contributes only instrumentally to well-being, mental health is more like bodily health, and a surprisingly small number of possible conditions count as mental health problems. I offer some arguments in favour of the second view, making use of my own opinions about well-being and a story about mental health recently defended by Nomy Arpaly. I also suggest that strategies for resolving the conflict between subjectivist and objectivist conceptions of well-being might be employed to help us find some attractive middle ground between naturalist and constructivist conceptions of mental health.