Extracorporeal membrane oxygenation (ECMO) is an adaptation of conventional cardiopulmonary bypass techniques to provide cardiopulmonary support. ECMO provides physiologic cardiopulmonary support to aid reversible aspects of the disease process and to allow recovery. ECMO does not provide treatment of the underlying disease. The indications for ECMO support have expanded from acute respiratory failure to acute cardiac failure refractory to conventional treatments from wide patient subsets involving neonates to adults. Vascular access for ECMO support is either percutaneous through a single-site, dual-lumen bicaval cannula or transthoracic via separate cannulas. The modes of support are either veno-venous or veno-arterial ECMO. In this article, the physiologic aspects of ECMO support are outlined.