Resuscitative ultrasonography provides rapid, repeatable, and multisystem assessment to guide diagnosis and management of critically ill patients in the emergency department (ED). Cardiac ultrasonography offers new anatomic and hemodynamic information, previously unavailable in an ED setting, whereas other applications match or exceed the speed and utility of existing tests such as chest radiograph (thoracic ultrasonography) or central venous pressure determination (inferior vena cava ultrasonography). Evolving areas of resuscitative ultrasonography include neurologic applications and transesophageal echocardiography, which promise to further enhance the role of ultrasonography in managing critical illness in the ED.