In the USA, injury is the leading cause of death among individuals between the ages of 1 and 44 years, and the third leading cause of death overall. Approximately 20 to 40% of trauma deaths occurring after hospital admission are related to massive hemorrhage and are potentially preventable with rapid hemorrhage control and improved resuscitation techniques. Over the past decade, the treatment of this population has transitioned into a damage control strategy with the development of resuscitation strategies that emphasize permissive hypotension, limited crystalloid administration, early balanced blood product transfusion, and rapid hemorrhage control. This resuscitation approach initially attempts to replicate whole blood transfusion, utilizing an empiric 1:1:1 ratio of plasma:platelets:red blood cells, and then transitions, when bleeding slows, to a goal-directed approach to reverse coagulopathy based on viscoelastic assays. Traditional resuscitation strategies with crystalloid fluids are appropriate for the minimally injured patient who presents without shock or ongoing bleeding. This chapter focuses on the assessment and resuscitation of seriously injured trauma patients who present with ongoing blood loss and hemorrhagic shock.