Traumatic brain injury is relatively common in military and law enforcement activities, despite ongoing improvements in head protection gear and in medical aid procedures and evacuation equipment in battlefield and conflict scenarios. In this chapter, we provide the relevant anatomical and physiological background which is relevant for understanding the occurrence and consequences of a traumatic brain injury and its subcategories. Next, we review the biomechanics of traumatic brain injury, and describe biomechanical injury criteria and thresholds. Finally, we introduce the concepts of modelling brain injuries by means of finite element techniques which consider the biomechanical properties of the head and neck tissues. The possible applications of such computational modelling and simulations, particularly for developing and testing military head-protection equipment, are discussed as well.