Capacitors are passive components that play an essential role in electronic circuits. Based on a principle first formulated in the 18th century, capacitors store electrical charge, acting as a kind of battery. However, unlike a battery they release their charge immediately and do not replenish their supply. Capacitors block the flow of direct current while allowing alternating current to pass through the circuit. The components consist of a pair of conductors separated by a dielectric.

The amount of electrical charge stored by an individual component is called capacitance and measured in farads, named after the British physicist Michael Faraday. Capacitance is written as a numerical value in the form of F (farad). Because a farad is a very high figure, capacitance values are expressed as submultiples of a farad, in the form µF (MicroFarad or millionth of 1 Farad), nF (NanoFarad or billionth of 1 Farad) or pF (PicoFarad or trillionth of 1 Farad).

There are many different types of capacitor, defined usually by its polarisation, the material used in its manufacture, such as Ceramic, Tantalum and Polyester, and the way it is mounted onto the circuit board.

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