Cranial electrical stimulation (CES) is a non-invasive method of applying low-intensity electrical current to the head. It is related to but distinct from other forms of transcranial electrical stimulation including electroconvulsive therapy, transcranial direct current stimulation (tDCS), and high-definition transcranial direct current stimulation. The different versions of transcranial electrical stimulation vary in the placement of electrodes, the intensity of the current, and the waveform of the current. According to Guleyupoglu and colleagues, CES evolved from the concept of “electrosleep,” first investigated at the beginning of the 20th century. Most of the early research and applications occurred in Russia. Beginning in the 1960s, the concept of electrosleep became more popular in the USA. Because of the belief that the treatment did not actually induce sleep, but rather the sleep was a side effect of the relaxing effect of the current stimulation, the name was changed from “electrosleep” to “cranial electrical stimulation.” Other proposed names, which have not persisted, included “transcerebral electrotherapy” and “NeuroElectric Therapy.” The latter is noteworthy because it gave its name to an early CES device, the Neurotone 101, which was the first device approved by the FDA. All subsequent CES devices have been cleared for marketing by FDA based on the concept of claiming equivalency to the Neurotone 101. The status of cranial electrical stimulation devices and FDA regulation remains a matter of some controversy.