Reviews the literature since 1967 on subjective well-being (SWB [including happiness, life satisfaction, and positive affect]) in 3 areas: measurement, causal factors, and theory. Most measures of SWB correlate moderately with each other and have adequate temporal reliability and internal consistency; the global concept of happiness is being replaced with more specific and well-defined concepts, and measuring instruments are being developed with theoretical advances; multi-item scales are promising but need adequate testing. SWB is probably determined by a large number of factors that can be conceptualized at several levels of analysis, and it may be unrealistic to hope that a few variables will be of overwhelming importance. Several psychological theories related to happiness have been proposed; they include telic, pleasure and pain, activity, top–down vs bottom–up, associanistic, and judgment theories. It is suggested that there is a great need to more closely connect theory and research.