Undoubtedly, few social scientists today think that the mass media have the power to sway huge audiences to the extent once believed likely. Nevertheless, the technological advances of the last century-from the first primitive radio broadcasts to today’s high speed mobile Internet devices-have made it possible for individual communicators to have access to unprecedented numbers of potential message recipients, and recipients to a constant barrage of messages. Millions of dollars are spent worldwide each year in attempts to change peoples’ attitudes about political candidates, consumer products, health and safety practices, and charitable causes. In most of these instances, the ultimate goal is to influence people’s behavior so that they will vote for certain politicians or referenda, purchase specific goods, engage in safer driving, eating, and sexual activities, and donate money to various religious, environmental, and educational organizations and institutions. To what extent are media persuasion attempts effective?