The pleura is part of the respiratory system. It is the serous membrane that lines the inside of the chest wall and delimits a space between the lungs on the inside (which it envelops) and the rib cage on the outside. The pleura is composed of 2 layers. A distinction is made between the parietal pleura, located against the chest wall, and the visceral pleura or pulmonary pleura, attached to the lungs. The two layers are separated by an empty space called the pleural cavity. The two pleural cavities (right and left) are not connected to each other. The layers of the two pleura meet in different pleural sinuses. Like all serous membranes, they have a role in reducing friction caused by movement (respiratory movement in this case). They are lined by an epithelium that secretes a small quantity of lubricating liquid.

The pleura helps protect the lungs by reducing the impact of shocks and blocking the passage of certain viruses and bacteria. If there is fluid in the pleura, it is called pleurisy. If air is present, it is called a pneumothorax.