A self-contained breathing apparatus (SCBA), sometimes referred to as a compressed air breathing apparatus (CABA) or simply breathing apparatus (BA), is a device worn to provide breathable air in an atmosphere that is immediately dangerous to life or health. They are typically used in firefighting and industry.

The term self-contained means that the SCBA is not dependent on a remote supply of breathing gas (e.g., through a long hose). If designed for use underwater, it is also known as a Scuba set (self-contained underwater breathing apparatus). When not used underwater, they are sometimes called industrial breathing sets. Unofficial names include air pack, air tank, oxygen cylinder, or simply pack, which are mostly used in firefighting.

An SCBA typically has three main components: a high-pressure tank (e.g., 2,216 to 5,500 psi (15,280 to 37,920 kPa), about 150 to 374 atmospheres), a pressure regulator, and an inhalation connection (mouthpiece, mouth mask or face mask), connected together and mounted to a carrying frame.

A self-contained breathing apparatus may fall into one of two categories: open-circuit or closed-circuit.