Many tools are nowadays available to monitor patients' hemodynamics in the intensive care unit (ICU) and in the operating room (OR) settings. Some monitoring tools are invasive such as the pulmonary artery catheter (PAC), some others are less invasive such as transpulmonary thermodilution (TPD) systems, some others are called minimally invasive such as uncalibrated arterial pulse wave analysis (PWA) devices, and some others are non invasive such as volume-clamp method, applanation tonometry, esophageal Doppler, bioreactance, CO2 rebreathing, and pulse wave transit time. Recently, the European Society of Intensive Care Medicine has provided recommendations about the use of hemodynamic monitoring in patients with shock. To summarize, except the PAC and the TPD systems, the other hemodynamic monitoring tools are not recommended for the two following reasons: 1) they provide cardiac output but not other important hemodynamic variables, although some of them also provide stroke volume variation (SVV) or pulse pressure variation (PPV), and 2) their validity has been questioned in cases of shock requiring vasopressors. The uncalibrated PWA devices or esophageal Doppler seem to be more suitable in the OR setting when no vasopressor is used. The advantage of the PAC is to provide pulmonary artery pressure and pulmonary artery occlusion pressure. The advantage of TPD systems is to provide global end-diastolic volume (a measure of global cardiac preload), extravascular lung water (a measure of lung edema), pulmonary vascular permeability index (a measure of lung capillary leak), cardiac function index (a measure of systolic cardiac function), PPV and SVV (dynamic indices of fluid responsiveness). The PAC and TPD systems are indicated in cases of shock either when the patient also has a severe ARDS initially or when the shock state does sufficiently respond to the initial therapy administered on the basis of clinical examination, central venous oxygen saturation, carbon dioxide pressure gap, PPV and echocardiography.