Magnetic flux controllers are materials other than the copper coil that are used in induction systems to alter the flow of the magnetic field. This article describes the effects of magnetic flux controllers on common coil styles, namely, outer diameter coils, inner diameter coils, and linear coils. It provides information on the role of magnetic flux controllers for whole-body and local area mass-heating applications, continuous induction tube welding, seam-annealing inductors, and various induction melting systems, namely, channel-type, crucible-type, and cold crucible systems. The article also describes the benefits of the flux controllers for induction heat treating processes such as single-shot and scanning.