Depressed individuals show altered responding to positive events relative to healthy individuals. This altered responding predicts greater symptom severity and functional impairment, and is not adequately addressed in current treatments. The present research aimed to utilize recent advances in the field to develop a more sophisticated understanding of positive event reactivity in depression. Chapter 1 evaluated responses to daily positive events in individuals with major depression and generalized anxiety disorder. In contrast to studies conducted in the lab, which typically find blunted responses to positive stimuli in depression, depressed individuals showed larger changes in emotions, cognitions, withdrawal behaviors, and symptoms than healthy controls following positive events in daily life. These changes were largely specific to depression relative to anxiety. This chapter highlights the importance of context when measuring responding to positive events, as well as the importance of considering outcomes beyond emotion and examining the role of co-occurring anxiety. In Chapter 2, the Positive Valence Systems Scale (PVSS) was developed to provide a broad assessment of responding to positive events. The scale measures the major types of events and phases of event responding delineated in recent research. The PVSS showed evidence of internal consistency, retest reliability, and convergent and discriminant validity, and was more closely related to depression than anxiety. Chapter 2 supplies the field with a more nuanced measure of responding to positive events that can be used to assess altered reactivity across diagnostic boundaries. Chapter 3 evaluated emotional reactions to future, as well as past, positive events in depression and examined cognitive responses hypothesized to enhance or dampen these reactions. Depressed individuals reported greater use of dampening responses than controls, but similar levels of enhancing responses. Results point to specific cognitive responses that predict emotional reactivity to positive events and may play a role in explaining altered reactivity in depressed individuals. Collectively, these studies demonstrate the importance of context in understanding reactivity to positive events in depression, propose that differences in reactivity are relatively specific to depression vis-à-vis anxiety, and identify cognitive processes that may help explain altered emotional responding in depression.