Atelectasis is defined as an alveolar collapse due to lack of airfilling. In newborns there exists a condition of primary atelectasis (after delivery, before the first breath). Secondary atelectasis can occur at any age after birth. Many causes are known such as malformations, aspiration, pulmonary hypertension, and others. Emphysema is defined as an enlargement of alveolar spaces combined with the destruction and remodeling of the alveolar septa usually resulting also in numerical loss of alveoli. A simple enlargement without destruction is not emphysema, but hyperinsufflation is seen in status asthmaticus. Several causes are known for emphysema, such as α1-antitrypsin deficiency, cigarette smoking, fibrosis, and scarring. Emphysema has several dismal consequences, and the most important is reduced oxygenation of the blood. A new focus on emphysema research has focused on the role of macrophages and lymphocytes and on aspects of autoimmunity.