Some uses of capacitors are energy storage, power conditioning, motor starters, suppression and coupling, signal processing, sensing, and supplying pulsed power. Capacitors have many uses in electrical and electronic systems.

A capacitor is used for storing energy by connecting it to its charging circuit. When disconnected from its charging circuit, it then dissipates the stored energy. A capacitor can, therefore, be used as a temporary battery. Capacitors are mostly used to maintain power supply when electronic devices are being charged. In motor vehicle audio systems, large capacitors store energy for the amplifiers to use.

Capacitor banks, which are low-inductance, high-voltage capacitors, are used for supplying huge pulses of current to pulsed power applications, such as Marx generators, particle accelerators, fusion research, electromagnetic forming and pulsed lasers. Large capacitor banks, commonly known as reservoirs, are mainly used as energy sources for slapper detonators or exploding bridgewire detonators in nuclear weapons.

Reservoir capacitors are used to smooth the output of half- or full-wave rectifiers in power supplies. They are also used for power factor correction in electric power distribution.

Capacitors are often used to separate the DC and AC components of signals because they can pass AC signals and block DC signals. This process is known as capacitive, or AC, coupling. A decoupling capacitor can also be used for decoupling one part of a circuit from another.