This diary study examined the proposal that satisfaction of two psychological needs, competence and autonomy, leads to daily well-being. Between-subjects analyses indicated that participants higher in trait competence and trait autonomy tended to have "better" days on average. Independently, within-subject analyses showed that good days were those in which participants felt more competent and autonomous in their daily activities, relative to their own baselines. Other predictors of daily well-being included gender, whether the day fell on a weekend, and the amount of negative affect and physical symptomatology felt the day before. Although past diary studies have tended to focus on threats to daily well-being, the authors suggest that psychological need concepts offer promise for understanding its positive sources.