Over the past century, the treatment of various forms of circulatory shock has included fluid resuscitation with either crystalloidal or colloidal solutions. Despite decades of investigation, there still is considerable controversy over the beneficial and adverse effects of each fluid type. Most authors agree that the initial resuscitation of any form of shock should be performed with crystalloid solutions. Trauma resuscitation uses crystalloid therapy almost exclusively. Much controversy exists when the shock state involves increased microvascular permeability, such as seen in sepsis, anaphylaxis, and burns. Concerns involve increased permeability pulmonary edema and whether colloid or crystalloid therapy may contribute to its formation. Regardless of fluid type used for resuscitative efforts, it is essential to ensure adequate invasive and noninvasive monitoring to guide therapy. Endpoints to resuscitation should include stabilization of vital signs, adequate urine output, adequate cardiac output, and evidence of supply-independent oxygen consumption. Side effects of aggressive fluid loading are frequent and include intravascular volume overload, pulmonary edema, increased myocardial water content, brain swelling, gastrointestinal ischemia, and massive systemic edema. These complications can best be minimized by careful fluid titration, using physiologic and hemodynamic endpoints.