The goal of this study was to identify and provide a detailed description of thoracic injury mechanisms, loading directions, and injury sources for rollover crash-involved occupants. As part of a larger effort to investigate dynamic rollover crash testing as a means of evaluating vehicle- specific occupant injury risk, the types, mechanisms and sources of thoracic injuries need to be well defined to provide metrics for evaluating injury risk in rollover crashes and computational simulations and to evaluate the ability of existing injury criteria to predict thoracic injuries. The thorax was found to be the most commonly injured body region, at the AIS 3+ level, for belted, not-ejected occupants involved in rollover crashes where the rollover was the most harmful event. Thoracic injuries are typically the result of direct lateral (impact) loading to the thorax by the interior of the vehicle, which results from when the right or left sides of the vehicle impact the ground during the crash.