Electroreception and electrogenesis are the closely related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes, such as the electric eel, to stun prey. The capabilities are found almost exclusively in aquatic or amphibious animals, since water is a much better conductor of electricity than air. In passive electrolocation, objects such as prey are detected by sensing the electric fields they create. In active electrolocation, fish generate a weak electric field and sense the different distortions of that field created by objects that conduct or resist electricity. Active electrolocation is practised by two groups of weakly electric fish, the order Gymnotiformes (knifefishes) and family Mormyridae (elephantfishes), and by the monotypic genus Gymnarchus (African knifefish). An electric fish generates an electric field using an electric organ, modified from muscles in its tail. The field is called weak if it is only enough to detect prey, and strong if it is powerful enough to stun or kill. The field may be in brief pulses, as in the elephantfishes, or a continuous wave, as in the knifefishes. Some strongly electric fish, such as the electric eel, locate prey by generating a weak electric field, and then discharge their electric organs strongly to stun the prey; other strongly electric fish, such as the electric ray, electrolocate passively. The stargazers are unique in being strongly electric but not using electrolocation.

The electroreceptive ampullae of Lorenzini evolved early in the history of the vertebrates; they are found in both cartilaginous fishes such as sharks, and in bony fishes such as coelacanths and sturgeons, and must therefore be ancient. Most bony fishes have secondarily lost their ampullae of Lorenzini, but other non-homologous electroreceptors have repeatedly evolved, including in two groups of mammals, the monotremes (platypus and echidnas) and the cetaceans (Guiana dolphin).

In 1678, while doing dissections of sharks, the Italian physician Stefano Lorenzini discovered organs on their heads now called ampullae of Lorenzini. He published his findings in Osservazioni intorno alle torpedini. The electroreceptive function of these organs was established by R. W. Murray in 1960.

In 1921, the German anatomist Viktor Franz described the knollenorgans (tuberous organs) in the skin of the elephantfishes, again without knowledge of their function as electroreceptors.

In 1949, the Ukrainian-British zoologist Hans Lissmann noticed that the African knife fish (Gymnarchus niloticus) was able to swim backwards at the same speed and with the same dexterity around obstacles as when it swam forwards, avoiding collisions. He demonstrated in 1950 that the fish was producing a variable electric field, and that the fish reacted to any change in the electric field around it.

Electroreceptive animals use the sense to locate objects around them. This is important in ecological niches where the animal cannot depend on vision: for example in caves, in murky water, and at night. Electrolocation can be passive, sensing electric fields such as those generated by the muscle movements of buried prey, or active, the electrogenic predator generating a weak electric field to allow it to distinguish between conducting and non-conducting objects in its vicinity.

In passive electrolocation, the animal senses the weak bioelectric fields generated by other animals and uses it to locate them. These electric fields are generated by all animals due to the activity of their nerves and muscles. A second source of electric fields in fish is the ion pump associated with osmoregulation at the gill membrane. This field is modulated by the opening and closing of the mouth and gill slits. Passive electroreception usually relies upon ampullary receptors such as ampullae of Lorenzini which are sensitive to low frequency stimuli, below 50 Hz. These receptors have a jelly-filled canal leading from the sensory receptors to the skin surface.

In active electrolocation, the animal senses its surrounding environment by generating weak electric fields (electrogenesis) and detecting distortions in these fields using electroreceptor organs. This electric field is generated by means of a specialised electric organ consisting of modified muscle or nerves. Animals that use active electroreception include the weakly electric fish, which either generate small electrical pulses (termed "pulse-type"), as in the Mormyridae, or produce a quasi-sinusoidal discharge from the electric organ (termed "wave-type"), as in the Gymnotidae.