The article develops a theory of demand for insurance that emphasizes the interaction between market insurance, “self-insurance,” and “self-protection.” The effects of changes in “prices,” income, and other variables on the demand for these alternative forms of insurance are alalyzed using the “state preference” approach to behavior under uncertainty. Market insurance and self-insurance are shown to be substitutes, but market insurance and self-protection can be complements. The analysis challenges the notion that “moral hazard” is an inevitable consequence of market insurance, by showing that under certain conditions the latter may lead to a reduction in the probabilities of hazardous events.