Mechanical ventilation of the lungs is an integral component of modern medical practice in the operating room and intensive care unit settings. Most ventilators available in the operating room are capable of providing only controlled mechanical ventilation. With the increasing use of the microprocessor-controlled ventilators in the intensive care unit, there are now a wide variety of ventilatory types and mode choices available to the clinician. This paper summarizes some of the ventilatory choices currently available and mentions some of the newer and experimental modalities available in larger centers.