An important contribution of social psychology to legal and political scholarship has been to provide a theory and supportive evidence for procedure-based legitimacy. The capacity of fair procedures to legitimate the right of an authority to make decisions for a group is central to the viability of democracies and pluralistic societies. It is not at all obvious that people would weigh concerns about justice over judgments about their self-interest or that they would focus on procedural justice in addition to or instead of distributive justice (“just deserts” or “deservedness”). In recent decades, a body of social science scholarship has generally demonstrated that people care about justice. Beyond that, research supports the viability of procedural justice in particular when dealing with authorities. As a result, procedural justice-based legal and political legitimacy has grown dramatically supporting a social psychological model of authority. At the same time that a body of social science evidence in favor of procedural justice and legitimacy has been growing, societal forces that might challenge the viability of legitimacy-based law and governance have become more prominent. These include the rise of more extreme liberal and conservative ideologies and/or the existence of and growth in autocratic (authoritarian or antidemocratic) values. This chapter examines the impact of these factors on the viability of procedural justice-based legitimacy. It does so both in the context of specific elections as well as in general evaluations of government. The findings are both reassuring and concerning. On the one hand, procedural justice is and continues to be a strong factor underpinning the legitimacy of authorities. On the other hand, both extreme ideologies and autocratic values lessen the influence of procedural justice on legitimacy and hence undermine the viability of legitimacy-based authority. These findings suggest that increases in either extreme ideologies or autocratic values do threaten pluralistic democracies.