Mechanisms by which personality affects well-being are not well understood. Following recommendations to examine intermediate process variables that may help explain the personality–subjective well-being (SWB) relationship, the authors tested whether constructive thinking (CT) mediated the relationships between both neuroticism and extraversion and SWB components. Measures of each construct were administered to 147 undergraduate volunteers twice over four weeks. In analyses controlling for time 1 SWB and time 2 mood, time 2 CT fully mediated the relationship between time 1 neuroticism and time 2 negative affect and emerged as a strong predictor of negative affect (inversely), positive affect, and happiness. Copyright © 2005 John Wiley & Sons, Ltd.