This chapter reviews the scientific research on subjective well-being. Subjective well-being consists of a person's cognitive and affective evaluations of his or her life. First, the authors will provide a brief historical review of research on subjective well-being. Second, they will summarize the main measurement issues (e.g., the validity of self-reports, memory bias). Third, they will present the major theoretical approaches to this area of research (e.g., need and goal satisfaction theories, process or activity theories, genetic and personality predisposition theories). Finally, the authors will review current findings (e.g., hedonic adaptation, the effect of intervention, cultural variation) and suggest future directions for the study of subjective well-being.