The current study examined vulnerability to depression during the transition from early to middle adolescence from the perspective of the response styles theory. During an initial assessment, 382 adolescents (ages 11-15 years) completed self-report measures assessing rumination and depressive symptoms as well as a semistructured clinical interview assessing current and past major depressive episodes. Every 3 months for the subsequent 2 years, adolescents completed self-report measures assessing depressive symptoms and negative events. Every 6 months, adolescents completed a semistructured clinical interview assessing the onset of new major depressive episodes. Higher levels of rumination were associated with a greater likelihood of exhibiting a past history of major depressive episodes, a greater likelihood of experiencing the onset of a future major depressive episode, and greater duration of future depressive episodes. Consistent with a vulnerability-stress perspective, rumination moderated the association between the occurrence of negative events and the development of future depressive symptoms and major depressive episodes.