If self-regulation conforms to an energy or strength model, then self-control should be impaired by prior exertion. In Study 1, trying to regulate one's emotional response to an upsetting movie was followed by a decrease in physical stamina. In Study 2, suppressing forbidden thoughts led to a subsequent tendency to give up quickly on unsolvable anagrams. In Study 3, suppressing thoughts impaired subsequent efforts to control the expression of amusement and enjoyment. In Study 4, autobiographical accounts of successful versus failed emotional control linked prior regulatory demands and fatigue to self-regulatory failure. A strength model of self-regulation fits the data better than activation, priming, skill, or constant capacity models of self-regulation.The capacity of the human organism to override, interrupt, and otherwise alter its own responses is one of the most dramatic and impressive functions of human selfhood, with broad implications for a wide range of behavior patterns (Carver & Scheier, 1981;Wegner & Pennebaker, 1993). For example, self-regulation has been associated with crime and criminal behavior (Gottfredson & Hirschi, 1990), smoking (Russell, 1971), and dieting (Herman & Polivy, 1975). Men with better self-control are less likely to become divorced (Kelly & Conley, 1987). Children who are better at delaying gratification tend to be calmer, to resist frustration better, to be less irritable and aggressive, to concentrate better, and to get higher grades in school than children who are less able to delay gratification (Funder & Block, 1989;Funder, Block, & Block, 1983). Additionally, children who were better able to control themselves could deal with stress better in adolescence and had higher SAT scores when applying to college (Shoda, Mischel, & Peake, 1990). It is clear that self-control is related to success in many aspects of life.Furthermore, the failure of self-control has immense personal and societal repercussions (Baumeister, Heatherton, & Tice, 1994). Breakdowns in self-control are linked with depression (Beck, 1976;Pyszczynski, Holt, & Greenberg, 1987;Wenzlaff, Wegner, & Roper, 1988), obsessive or ruminative thoughts (Martin & Tesser, 1989;Wegner, Schneider, Carter, & White, 1987), and aggression (Baumeister, 1997;Gottfredson & Hirschi, 1990;Tice & Baumeister, 1993;Zillman, 1993). concluded that many of the problems facing both individuals and society today, ranging from unprotected sexual behavior to addiction to school underachievement, involve regulatory failure. Therefore a deeper understanding of how, why, and when self-control breaks down is highly desirable.The purpose of this article is to examine one central reason why self-control may fail. We propose that people have a limited capacity for self-regulation, akin to having a limited supply of strength or energy. One central prediction of any such model is that exertion will be followed by a period of diminished capacity. Therefore, when people engage in self-regulation, they should show subsequent decrements on other tasks ...