Oxygen therapy involves delivering oxygen concentrations above 21% to address hypoxemia or hypoxia. Various oxygen delivery systems can be used, ranging from low-flow nasal cannulas to high-flow venturi masks and non-rebreathing masks. Complications of prolonged high-concentration oxygen therapy include hypoventilation, absorption atelectasis, pulmonary toxicity, and retrolental fibroplasia in premature infants. The appropriate oxygen concentration and delivery method depends on careful evaluation of each patient's condition and needs.