This paper describes the three-dimensional (3-D) modeling of an induction heating system. To realize the suitable construction of a high-frequency induction heating coil, numerical computations of eddy currents and heat conduction have been carried out by using the finite-element method (FEM) and also taking into account the dependence of material properties on temperature. For a high-frequency induction heating coil, which is normally applicable for heat treatment, the tubular solenoid design is the most appropriate due to its high coil efficiency. Coil efficiency is that part of energy delivered to the coil, which is transferred to the workpiece. Besides coil efficiency, the heating pattern and the production rate are also important. As the heating pattern reflects the coil geometry, optimal coil design is a prerequisite to attain the desired heating. Several modifications, such as spacing in between coil turns, the motion of the workpiece relative to the coil, and dimensional parameters, were carried out until optimal design was achieved.