The personality trait extraversion is associated with higher positive affect, and individuals who behave in an extraverted way experience increased positive affect. Across 2 studies, we examine whether the positive affectivity of extraverts can be explained in terms of qualitative aspects of social experience resulting from extraverted (i.e., bold, assertive) behavior. In our first study (N = 225, 58% female), we found that social well-being, a broad measure of quality of social life (Keyes, 1998) was a significant mediator of the relation between trait extraversion and trait positive affect. This effect was specific to 1 aspect of social well-being—social contribution, one’s sense of making an impact on one’s social world. In our second study (N = 81, 75% female), we found that a momentary assessment of social well-being mediated the effect of experimentally manipulated extraverted behavior (in the context of 2 brief discussion tasks) on state positive affect. Furthermore, perceived contribution to the discussion tasks accounted for up to 70% of the effect of enacted extraversion on positive affect. This is the first identified mediator of the effect of enacted extraversion on positive affect. Implications and suggestions for extensions of this research are discussed.