Past research has demonstrated a relationship between happiness and workplace success. For example, compared with their less happy peers, happy people earn more money, display superior performance, and perform more helpful acts. Researchers have often assumed that an employee is happy and satisfied because he or she is successful. In this article, the authors review evidence in support of an alternative hypothesis--namely, that happiness is a source of why particular employees are more successful than others. To this end, the authors consider evidence from three types of studies--cross-sectional, longitudinal, and experimental--that relate happiness to various work outcomes. Taken together, the evidence suggests that happiness is not only correlated with workplace success but that happiness often precedes measures of success and that induction of positive affect leads to improved workplace outcomes.