The objective of this dissertation was to systematically investigate the pattern, causation, mechanism and mitigation of neck injuries during rollover crashes by field data analyses and finite element (FE) simulations. A survey of the field data from NASS-CDS database was first conducted. Results showed that neck was the third commonly injured body region, following the head and chest, in rollovers, and roof was the major coded-source of head and neck injuries during rollover crashes. A weighted logistic regression analysis of the NASS-CDS data further showed that occupant age, weight, number of quarter turns and vertical roof deformation adjacent to the occupant were significant predictors of neck injury odds for belted occupants. On the other hand, our rollover simulations using a set of state-of-the-art FE vehicle, restraint system, dummy, and human models indicated that roof deformation did not cause the head and neck injuries. The high head acceleration and neck load were mainly caused by the inertia of the occupant’s torso compressing the head into the roof before any significant roof deformation occurred. Our simulated dummy responses also showed that the stiffness of the near-side roof did affect the head and neck injury risks in certain impact mode, in which the stronger the roof, the lower the injury risks, although our simulated human responses did not show the same trend. Simulations using a detailed head-neck FE model under conditions similar to real rollover scenarios demonstrated that impact velocity was the most important factor in determining the neck injury risk. Coefficient of friction (COF) also played an important role. As long as the COF was in a low level, padding could decrease the neck injury risk. To reduce the impact velocity between the head and the roof, seatbelt may play a very important role. Therefore, further FE simulations were performed to determine the effects of different design factors of a traditional three-point seatbelt system on limiting the occupant head excursions during dynamic rolling tests. Some general trends were recommended to design a more effective seatbelt for rollover crashes.