Execution by electrocution, performed using an electric chair, is a method of execution originating in the United States in which the condemned person is strapped to a specially built wooden chair and electrocuted through electrodes fastened on the head and leg. This execution method, conceived in 1881 by a Buffalo, New York, dentist named Alfred P. Southwick, was developed throughout the 1880s as a "humane alternative" to hanging, and first used in 1890. This execution method has been used in the United States and for a period of several decades,^[​1] in the Philippines. While death was originally theorized to result from damage to the brain, it was eventually shown in 1899 that it primarily results from ventricular fibrillation and eventual cardiac arrest.^[​2]

Once the person was attached to the chair, various cycles (changes in voltage and duration) of alternating current would be passed through the individual's body in order to cause fatal damage to the internal organs. The first, more powerful jolt of electric current is intended to cause immediate unconsciousness,^[​3][​2] ventricular fibrillation, and eventual cardiac arrest.^[​2] The second, less powerful jolt is intended to cause fatal damage to the vital organs.^[​2]

Although the electric chair has long been a symbol of the death penalty in the United States, its use is in decline due to the rise of lethal injection, which is widely believed to be a more humane method of execution. While some states still maintain electrocution as a method of execution, today it is only maintained as a secondary method that may be chosen over lethal injection at the request of the prisoner, except in Tennessee, where it may be used without input from the prisoner if the drugs for lethal injection are not available.^[​4] As of 2014, electrocution is an optional form of execution in the states of Alabama, Florida, South Carolina, and Virginia, all of which allow the prisoner to choose lethal injection as an alternative method. In the state of Kentucky, the electric chair has been retired, except for those whose capital crimes were committed prior to March 31, 1998, and who choose electrocution; inmates who do not choose electrocution and inmates who committed their crimes after the designated date are executed by lethal injection. Electrocution is also authorized in Kentucky in the event that lethal injection is found unconstitutional by a court.^[​5] The electric chair is an alternate form of execution approved for potential use in Arkansas, Mississippi, and Oklahoma if other forms of execution are found unconstitutional in the state at the time of execution.

On February 8, 2008, the Nebraska Supreme Court determined that execution by electric chair was a "cruel and unusual punishment" under the state's constitution. This brought executions of this type to an end in Nebraska, the only remaining state to retain electrocution as its sole method of execution.^[​6]