Shock is a common problem in the intensive care unit, requiring immediate diagnosis and treatment. It is usually defined by a combination of hemodynamic parameters (mean blood pressure <60 mm Hg, systolic blood pressure <90 mm Hg), clinical findings (altered mentation, decreased urine output), and abnormal laboratory values (elevated serum lactate, metabolic acidosis). The first step is to identify the cause of shock, as each condition will require different interventions. The overall goal of therapy is to reverse tissue hypoperfusion as quickly as possible in order to preserve organ function. Table 1.1 and Algorithms 1.1 and 1.2 offer an approach for determining the main cause of shock. Specific management of the various shock states is presented in the following chapters. Early evaluation with echocardiography, intraesophageal aortic waveform assessment, or right heart catheterization will allow determination of the cause of shock and will assist in management.