Critically ill patients are often unable to provide a clear history, the utility of the physical examination is limited by the patient's ability to cooperate, and the temporal and logistic impediments of diagnostic testing necessitate a limited, time-sensitive approach. With such critically ill patients, ultrasonography–which can identify many common causes of undifferentiated respiratory or circulatory compromise–can be applied to evaluate response to therapy and can deployed at the bedside within seconds is obviously of great value. This chapter discusses the use of bedside ultrasound in the management of the critically ill by intensivists, emergency physicians and paramedics, as well as care-providers in military, austere environment and natural-disaster settings. It presents a brief integrated review of the sonographic approach to the critically ill. The chapter focuses on the way that evaluation of individual organs or regions are combined with the management of syndromes of critical illness, namely airway, shock, dyspnoea and cardiopulmonary arrest.