The response styles theory (Nolen-Hoeksema, 1991) was proposed to explain the insidious relationship between rumination and depression. We review the aspects of the response styles theory that have been well-supported, including evidence that rumination exacerbates depression, enhances negative thinking, impairs problem solving, interferes with instrumental behavior, and erodes social support. Next, we address contradictory and new findings. Specifically, rumination appears to more consistently predict the onset of depression rather than the duration, but rumination interacts with negative cognitive styles to predict the duration of depressive symptoms. Contrary to original predictions, the use of positive distractions has not consistently been correlated with lower levels of depressive symptoms in correlational studies, although dozens of experimental studies show positive distractions relieve depressed mood. Further, evidence now suggests that rumination is associated with psychopathologies in addition to depression, including anxiety, binge eating, binge drinking, and self-harm. We discuss the relationships between rumination and worry and between rumination and other coping or emotion-regulation strategies. Finally, we highlight recent research on the distinction between rumination and more adaptive forms of self-reflection, on basic cognitive deficits or biases in rumination, on its neural and genetic correlates, and on possible interventions to combat rumination.