Mild traumatic brain injury (mTBI) has recently gained appreciation as a significant public health problem, which has highlighted just how little is known about its proximal and long-term effects. A major challenge in the study of mTBI is the heterogeneity of the condition. Research on mTBI has historically separated sport and nonsport etiologies, and the extent to which research from one of these samples translates to the other is unclear. This review examines the literature on mTBI, with a focus on comparing sport and nonsport etiologies with regard to the latest research on biomechanics, pathophysiology, neurocognitive effects, and neuroimaging. Issues of particular relevance to sports injuries, such as exercise, repetitive injuries, subconcussive blows, and chronic injury effects, are also reviewed.