A three-way switch is a type of electrical switch used to control a light fixture from two or more locations. It is larger than a single pole switch and has three screw terminals for wiring connections, plus a ground. Two of these take traveler wires that go from one switch to the other, while the third terminal is connected to either the hot supply wire or the light fixture. When both toggles are up or both are down, the circuit is complete and the light fixture will be illuminated. When the toggles are in opposite positions, the circuit is interrupted and the light fixture turns off. This allows either switch to control the on-off function of the light fixture at any time.

Three-way switches are commonly used to control one light fixture from two different locations, such as a long hallway or stairway with a switch at each end. They can also be used in combination with another type of switch, the four-way switch, to control light fixtures from three or more locations.

To identify a switch as being a three-way type, there are two clear giveaways: it has three terminals instead of two, and it lacks ON and OFF markings on its toggle. Three-way switches can be wired in a number of different ways, depending on where they are located relative to the light fixture in the circuit cable runs.