This paper suggests a way to think about human well-being and psychological health. It distinguishes between mental stocks and flows. Central to thenanalysis is a concept we refer to as hedonic capital. This can be thought of as a level of emotional coping resources, or as the underlying stock to which the economist’s idea of a flow of utility corresponds. The model replicates the patterns found in the recent empirical psychology and economics literature: there is an approximately stable level of mental well-being and an automatic tendency to adapt back towards that level. Conventional economic theory does not fit these facts.