We contribute to the understanding of marine reserves and the management of renewable resources with uncertainty. We show that the key benefit of reserves is that they increase resilience, or the speed it takes a population to return to a former state following a negative shock. Resilience can also increase resource rents even with optimal harvesting. We contradict the accepted wisdom that reserves have no value if harvesting is optimal, reserves and optimal output controls are equivalent, reserves have value only with overexploited populations and that reserves must be large to offer benefits to fishers.