Oxygen therapy for lung diseases is decided depending upon the type and chronicity of disease and the degree of hypoxemia. Requirements are greater for patients with acute illnesses or acute exacerbations of chronic illnesses. Chronic respiratory diseases with hypoxemia are usually benefitted by long term oxygen therapy. One should carefully consider the needs, the type and sensitivity of disease, and the factors related to oxygen transport, delivery and utilization for prescribing oxygen and defining the prescription-criteria. It is important to adopt the strategies tailored to the needs of a particular patient in different diseases such as chronic obstructive lung disease, bronchial asthma, interstitial lung disease, pulmonary infections, pulmonary hypertension, pulmonary thromboembolism and others.