Electrotherapy has an established role in the management of a wide range of musculoskeletal and neurological problems. Used in conjunction with other therapeutic interventions, it can make a positive contribution to patient care. The means by which a range of different exogenous energy forms can influence the physiological state of the tissue is well documented. Different therapeutic modalities achieve their effects in different tissues, and the clinical decision-making process should employ the available evidence in order to maximize the potential benefit for each patient. The applied energy essentially acts as a trigger that is responsible for stimulating, enhancing or activating particular physiological events, which in turn are utilized to achieve therapeutic benefit. There appear to be windows of opportunity related to the magnitude of the applied energy, the amplitude of the stimulus and the frequency of application. Tissues appear to vary in their responsiveness to these factors, and thus an appropriate modality applied in an inappropriate manner will fail to achieve the anticipated effect. This paper aims to review the current concepts of electrotherapy intervention, taking into account various theories which support the principles. Application of various energies in this way can result in significant benefit for the patient.