Do endocrine systems influence personality and social behavior? Although animal research has identified several hormone-behavior relationships and the mechanisms that give rise to them, much less is known about hormones and social functioning in humans. This dissertation used three large data sets to investigate whether testosterone and cortisol were related to variation in personality constructs (Study 1), leadership behaviors (Study 2), and economic decision making (Studies 3 and 4). Study 1 revealed that basal testosterone was negatively associated with conscientiousness, basal cortisol was negatively associated with extraversion but positively associated with social dominance orientation, and the interaction between testosterone and cortisol was associated with the implicit power motive. Study 2 found that the testosterone-cortisol interaction predicted leadership behaviors, and Study 3 showed that basal testosterone as well as change in cortisol predicted economic decisions in the Hawk-Dove Game. Finally, Study 4 demonstrated that aggression predicted decisions to punish unfair monetary offers in the Ultimatum and Third Party Punishment Games. Aggression was also related to women's changes in testosterone from before to after the games. Taken together, these studies provide important evidence that testosterone and cortisol are related to personality, leadership, and social decision making. More broadly, this dissertation lays the empirical foundation for further inquiry on the complex biological systems that regulate personality and social behavior.