An electric fence is a barrier that uses electric shocks to deter humans and animals from crossing a boundary. Most electric fences are used for agricultural purposes and other non-human animal control. They are also commonly used to protect high-security areas such as military installations or prisons, where a potentially lethal voltage may be applied. Virtual electric fences for livestock using GPS technology have also been developed.

Electric fences are designed to shock animals or humans if they attempt to cross a boundary. A component called a power energiser converts power into a brief high voltage pulse. One terminal of the power energiser releases an electrical pulse along a connected bare wire approximately once per second. Another terminal is connected to a metal rod implanted in the earth, called a ground or earth rod. An animal touching both the wire and the earth during a pulse would complete an electrical circuit, conducting a pulse, resulting in an electric shock. The effects of a shock depend upon the voltage, the energy of the pulse, the degree of contact between the recipient and the fence and ground, and the route of the current through the body; the severity of the shock can range from barely noticeable to lethal.

Most modern electric fences emit pulses of high voltage at a fixed time interval or use a voltage multiplier to store a high voltage that is applied continuously to the fence except when recharging after a shock.

Depending on the fenced area and the remoteness of its location, fence energisers may be hooked into a permanent electrical circuit or run by lead-acid or dry cell batteries or a smaller battery kept charged by a solar panel. The power consumption of a fence in good condition is low, and so a lead-acid battery powering several hundred metres of the fence may last for several weeks on a single charge. Certain energisers have the ability to be powered by multiple sources.

Early alternating current (AC) fence chargers used a transformer and a mechanically driven switch to generate the electrical pulses. The pulses were wide and the voltage unpredictable, with no-load peaks in excess of 10,000 volts and a rapid drop in voltage as the fence leakage increased, which had the liability of the switch mechanism failing. Later systems replaced this switch with a solid-state circuit. This circuit had an improvement in longevity but no change in pulse width or voltage control.

"Weed burner" fence chargers were popular for a time and featured a longer-duration output pulse that would destroy weeds touching the fence. These were responsible for many grass fires when used during dry weather. Although still available, they have declined in popularity.^{[citation needed]}

Smooth steel wire is the material most often used for electric fences, ranging from a fine thin wire used as a single line to thicker, high-tensile (HT) wire. Less often, woven wire or barbed wire fences can be electrified, though such practices create a more hazardous fence, particularly if an animal becomes caught by the fencing material, causing electrified barbed wire to be made unlawful in some areas. Synthetic webbing and rope-like fencing materials woven with fine conducting wires (usually of stainless steel) became available in the late 1990s and are particularly useful for areas requiring additional visibility or temporary fencing.

The electrified fence itself must be kept insulated from the earth and from any materials that will conduct electricity and ignite or short out the fence. Fencing must therefore avoid vegetation, and cannot be attached directly to wood or metal posts. Typically, wooden or metal posts are driven into the ground and plastic or porcelain insulators are attached to them, or plastic posts are used. The conducting material is then attached to the posts.