Happiness in the form of pleasant moods and emotions, well-being, and positive attitudes has been attracting increasing attention throughout psychology research. The interest in happiness has also extended to workplace experiences. This paper reviews what is known about the definition, causes and consequences of happiness at work, drawing also on insights from the expanding positive psychology literature on happiness in general. Many discrete organizational behavior constructs arguably belong to a larger family of happiness-related constructs, and share some common causes and consequences. Happiness at work includes, but is far more than, job satisfaction. A comprehensive measure of individual-level happiness might include work engagement, job satisfaction, and affective organizational commitment. Aspects of happiness have been (and should be) conceptualized and measured at multiple levels, including transient experiences, stable person-level attitudes, and collective attitudes, and with respect to multiple foci, such as discrete events, the job, and the organization. At all levels, there is evidence that happiness has important consequences for both individuals and organizations. Past research has tended to underestimate the importance of happiness at work.