A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When a potential difference (voltage) exists across the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the conductors. The effect is greatest when there is a narrow separation between large areas of conductors, hence capacitor conductors are often called plates. This book reviews research on the role of capacitors and capacitance within plasma processing; voltage stabilisation using a storage capacitor; disposal of PCB capacitors in Kazakhstan; and how ideal and real capacitors affect the behaviour of energy efficiencies.