This study investigates the modeling of the Hybrid III dummy head and neck system and its response under impulsive loading. Two neck models were proposed, one rigid, one flexible;​ both give satisfactory head kinematics upon comparing to minisled test results. The flexible neck model provides a more detailed understanding of the Hybrid III neck structure behavior. It indicates that the Hybrid III neck has a torque response similar to a human neck but has higher shear response. During flexion whiplash, the torque at the occipital condyle reverses its direction at about 25 ms after impact. Since concussion may be related to the head angular acceleration, which reaches its peak value in the first 25 ms. it might be necessary to extend the existing human torque-rotation corridor to include the neck response in this region. For flexion whiplash impact, simulation results indicated that the neck injury threshold is reached before exceeding the head injury threshold as the impact velocity is increased.