Coagulation abnormalities are common in critically ill patients. Intensive care unit (ICU) patients with abnormal coagulation have a four- to five-fold higher risk for bleeding compared to those with normal coagulation. The risk of intracranial hemorrhage in critically ill patients during ICU admission is relatively low (0.3–0.5%); 88% of patients with this complication have a platelet count below 100 × 109/L. Moreover, coagulation abnormalities may indicate ongoing coagulation activation, which plays a role in microvascular thrombosis, resulting in multiple organ failure. Rapid identification of these patients is important to provide adequate supportive therapeutic strategies. A myriad of altered coagulation parameters are often detectable, such as prolonged global coagulation times, reduced levels of coagulation inhibitors, and high levels of fibrin split products. These coagulation changes are often accompanied by a drop in platelet count. Proper identification of the underlying cause for these coagulation abnormalities is required, since various coagulation disorders may necessitate different diagnostic and therapeutic management strategies. This chapter reviews the most frequently occurring coagulation abnormalities in critically ill patients with emphasis on the differential diagnosis, the underlying pathophysiology, and the appropriate management.