Hemorrhage is the most common cause of shock in patients with polytrauma, leading to cellular hypoxia and death. A large body of experimental and clinical research has greatly expanded our knowledge of cellular mechanisms and clinical outcomes in resuscitation of patients with hypovolemic shock. However, the fundamental principles of fluid resuscitation have not changed during the past few decades. Aggressive resuscitation to correct tissue hypoperfusion within 24 hours of injury is associated with improved clinical outcomes. Initial volume expanders of choice are crystalloid solutions, with blood and blood products used for patients who are hemodynamically unstable, patients with Class III and Class IV hemorrhage, and patients with ongoing uncontrolled sources of bleeding. The incidence of immunologic and infectious complications associated with blood transfusions in resuscitation of patients with polytrauma has not been shown to be any higher than in other clinical settings. Massive resuscitations, however, are associated with specific complications such as hypothermia, coagulopathy, and abdominal compartment syndrome. Novel blood substitutes, hypertonic saline, and minimally invasive hemodynamic monitoring techniques have the potential of optimizing fluid resuscitation in patients with polytrauma. Additional research using standardized animal models and randomized clinical trials is needed.