In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to produce more power for a given displacement.

The history of turbochargers began in 1878 with the invention of mechanically-powered superchargers. The birth of the turbocharger is often attributed to Swiss engineer Alfred Büchi's 1905 patent, with the first prototype completed in 1915. Turbochargers were first used commercially in 1925, increasing the power output of diesel engines in two large passenger ships. During World War II, they were used in various aircraft engines, and Swiss truck manufacturer Saurer pioneered their use in the 1930s.

Turbochargers for passenger cars gained popularity in the 1980s, with the first models being the Chevrolet Corvair Monza and Oldsmobile Jetfire in 1962. The main components of a turbocharger include a turbine, compressor, and center housing hub rotating assembly. The turbine extracts kinetic energy from exhaust gases to power the compressor, which pressurizes intake air before entering the engine.

Twin-scroll turbochargers use two separate exhaust gas inlets to optimize exhaust gas flow, while variable-geometry turbochargers adjust the turbine housing geometry to maintain the optimum aspect ratio. Electrically-assisted turbochargers combine exhaust-powered turbines with electric motors to reduce turbo lag. The center hub rotating assembly connects the turbine to the compressor and may be water-cooled to protect the turbocharger's lubricating oil from overheating.

Turbochargers utilize additional components such as intercoolers, water injection, wastegates, and blowoff valves to improve engine performance. Turbo lag and boost threshold affect power delivery, and various methods can be employed to reduce turbo lag. Multiple turbochargers can be used to address these issues, with twin-turbo being the most common arrangement. Turbochargers differ from superchargers, as they are powered by exhaust gas instead of being mechanically driven by the engine. Twincharging combines both systems to mitigate their weaknesses. Turbochargers are used in various applications, including petrol and diesel engines, with increasing adoption in petrol engines. Safety concerns include turbocharger failures and high exhaust temperatures, which can cause car fires.

The current categorisation is that a turbocharger is powered by the kinetic energy of the exhaust gases, whereas a supercharger is mechanically powered (usually by a belt from the engine's crankshaft). However, up until the mid-20th century, a turbocharger was called a "turbosupercharger" and was considered a type of supercharger.