This book introduces a new breed of short-term electricity market-clearing problems which are subject to stochastic security criteria. The stochastic criteria are based on probabilistic measures of the expected load not served associated with the random failures of generators, transmission lines as well as variations in demand and wind power generation. Electricity markets gain in technical and economic flexibility as they get to balance the respective expected costs of preventive and corrective security actions necessary to counter the adverse effects of the random power system events. We illustrate how the principles of market-clearing with stochastic security can lead to non-negligible system security cost savings, while still ensuring that consumers benefit from a reliable supply of electricity in light of how they value the continuity of their electricity supply.