One of the most robust observations in personality and emotion research is the finding that extraverts are happier than introverts. Some theorists have attributed this to differential reactivity of the brain reward system, which is central to many biologically inspired models of extraversion. This affective-reactivity hypothesis, which suggests that extraverts should be more susceptible to the induction of positive affect, has so far received very mixed empirical support. In this article, we consider a more biologically plausible account of extraverts' affective-reactivity. Over 5 experiments, we demonstrate that extraverts show greater affective-reactivity only in response to clearly appetitive stimuli and situations (e.g., where rewards are being pursued). Conversely, after merely pleasant stimuli and situations (without any reward-approach element), extraverts and introverts respond similarly. We also show that it is specifically activated affect (e.g., feelings of alertness), rather than pleasantly valenced affect (e.g., feelings of contentment), that characterizes the affective-reactivity of extraverts. Such reactions may potentially facilitate the reward-seeking behavior associated with extraversion, but they seem unlikely to explain the broadly happy disposition of extraverts.