The pleura are the thin, double-layered, moist membranes that line the chest wall and cover the lungs.

Parietal pleura, the pleurae lining the chest, doubles back over at the root of the lung where it becomes known as the visceral pleura. The two membranes are really one continuous sheet of tissue. They enclose the narrow pleural cavity, a thin, slit-like space containing a friction-reducing fluid that lubricates the membranes and aides breathing. In normal health, this cavity or "pleural space" goes unnoticed. The cavity becomes apparent, however, when a lung collapses or air or liquid collects between membranes.

The parietal and visceral pleurae enclose each lung in a different sac. The parietal pleurae consist of one elastic layer and rest on the fibrocollagenous tissue attached to the ribs. Parietal pleurae are divided into four categories: costal, diaphragmatic, mediastinal, and cervical. They are all supplied by intercostal and phrenic nerves that allow this type of pleura to sense pain. The visceral pleura are made up of five elastic layers, one of which is irregular. Visceral pleura help form pulmonary ligaments and connect to the autonomic nerves.

Diseases of the pleura include pleurisy and pleural effusion. Pleurisy is an inflammation of the pleura characterized by a sharp, stabbing chest pain that becomes worse with deep breathing or coughing. Excess liquid in the pleural space results in pleural effusion, and can be the result of disease or trauma. Tumors of the pleura (mesothelioma) are seen most frequently in asbestos workers.