This research is concerned with why people view authorities as legitimate and voluntarily defer to them. While the effects of procedural fairness and outcome favorability on perceived legitimacy are already well established, this dissertation suggests the existence of another distinct contributor to legitimacy, namely, system justification motivation. I predicted that this motivation would emerge in settings in which people are dependent upon the authority for desired resources and tested this argument in seven studies, which were conducted in educational, political, organizational, and legal settings. Four field studies demonstrated that dependence on an authority figure is positively associated with appraisals of legitimacy. Dependence on an academic authority for conflict resolution predicted legitimacy perceptions among college students (Study 1), dependence on the government for the resource of water predicted legitimacy perceptions among Californian residents (Study 2), job dependence predicted employees' perceived legitimacy of their supervisor (Study 3), and dependence on the police predicted legitimacy perceptions among New York residents living in crime-ridden neighborhoods (Study 4). These effects were distinct from the influence of procedural fairness and outcome favorability, suggesting that both justice and justification mechanisms are at play in determining the perceived legitimacy of an authority. Three laboratory studies, further, provided direct causal evidence for the hypothesized effect on both perceived legitimacy and voluntary deference. Participants were told that their task performance would be evaluated and were assigned to a high or low outcome dependence condition. Participants assigned to the high dependence condition perceived the evaluator as more legitimate regardless of their treatment (Study 5) and were more likely to acquiesce to additional requests (Study 6). Supporting a motivational account of legitimation, these participants also judged their outcomes to be more favorable, despite the fact that the outcomes were identical in the two conditions; this effect was mediated by perceived legitimacy. The relationship between felt dependence and the perceived legitimacy of the evaluator was mediated by system justification (Study 7). The psychological dynamic I identify could contribute to the perpetuation of power inequalities, insofar as the powerless justify rather than try to change the structures of inequality that affect them.