Individual differences in the expression and regulation of emotion are important components of social skill. The present study focused on the concealing of spontaneous expressions of happiness after winning in a competitive situation against peers. In a repeated measures design, spontaneous expressive behaviors in response to triumph were secretly videotaped when Ss (N = 38) were alone in a room and when they were with 2 fellow competitors (confederates). Edited tapes were analyzed by naive raters and trained coders. As predicted, the social context strongly influenced the expressive behaviors of Ss, providing support for a social inhibition effect. More important, the self-monitoring construct (Snyder, 1987) was helpful in explaining individual differences in expressive regulation, with high self-monitors being successful at hiding their happiness when appropriate; and they did so in particular ways. Low self-monitors did not conceal their emotions. Other findings with regard to personality and sex differences were also uncovered.