Dictionary definitions of optimism encompass two related concepts. The first of these is a hopeful disposition or a conviction that good will ultimately prevail. The second, broader conception of optimism refers to the belief, or the inclination to believe, that the world is the best of all possible worlds. In psychological research, optimism has referred to hopeful expectations in a given situation and, recently, to general expectancies that are positive. Perhaps consistent with the second, broader definition of optimism, the terms optimism and pessimism have recently been applied to the ways in which people routinely think about causes of events in their lives. This article focuses on the explanatory style construct of optimism, presents some of the major research findings from this literature, and summarizes strategies for cultivating optimism in youth.