In science and engineering, conductors are materials that contain movable charges of electricity. When an electric potential difference is impressed across separate points on a conductor, the mobile charges within the conductor are forced to move, and an electric current between those points appears in accordance with Ohm's law. While many conductors are metallic, there are many non-metallic conductors as well. See electrical conduction for more information on the physical mechanism for charge flow in materials.

Under normal conditions, all materials offer some resistance to flowing charges, which generates heat. Thus, proper design of an electrical conductor includes an estimate of the temperature that the conductor is expected to endure without damage, as well as the quantity of electrical current. The motion of charges also creates an electromagnetic field around the conductor that exerts a mechanical force on the conductor. Consequently, a conductor of a given material and volume (length x cross-sectional area) has a limit to the current it can carry without being destroyed thermally or mechanically. This effect is especially critical in printed circuits, where conductors are relatively small.

Non-conducting materials lack mobile charges and are called insulators. A material can be an electrical conductor without being a thermal conductor, although a metal can be both an electrical conductor and a thermal conductor. Electrically conductive materials are usually classified according to their electrical resistance; ranging from high to null resistance, there are semiconductors, ordinary metallic conductors (also called normal metals ), and superconductors.

See conductor disambiguation for other meanings of conductor.