An electronic amplifier or amplifier is an electronic device used for increasing the power of a signal. It does this by taking energy from a power supply and controlling the output to match the input signal shape but with larger amplitude. In this sense, an amplifier may be considered as modulating the output of the power supply.

There are numerous types of electronic amplifiers specialized to various applications. An amplifier can refer to anything from an electrical circuit using a single active component to a complete system such as a packaged audio hi-fi amplifier.