Shock occurs when failure of the cardiovascular system compromises tissue perfusion. When fluid administration fails to restore adequate arterial pressure and organ perfusion in patients with shock, therapy with vasoactive agents should be initiated. The key to selecting among vasoactive agents is to make the choice in the context of the goals of therapy. The ultimate goals of hemodynamic therapy in shock are to restore effective tissue perfusion and to normalize cellular metabolism. The clinician needs to consider ways of achieving those goals and the mechanisms of action of potential therapies. Armed with this knowledge, it becomes easier to match the mechanism of action of a particular agent to the goals of therapy. When this is done, differences among various agents are seen primarily as differences in mechanisms of action, and discussions about which agent is "best" are transformed into consideration of which agent is best suited to implement the therapeutic strategy that has been selected in a given clinical context. Despite the complex pathophysiology of shock, use of vasoactive agents for hemodynamic support of patients with shock can be guided by an underlying approach in which clinicians define specific goals and end points, titrate therapies to those end points, and evaluate the results of their interventions on an ongoing basis.