Wireless power transfer (WPT) technology has been developed for the wireless charging of electric vehicles, consumer electronics, and other applications. Inductive power transfer (IPT) uses the magnetic field for power transfer and it is currently the most popular and mature WPT technology. However, the strong magnetic field will heat up metal objects falling in the charging area due to eddy currents generated in the objects. It can also harm animals or toddlers staying in the charging area. To deal with these issues, foreign object detection (FOD), including metal object detection (MOD) and living object detection (LOD), should be developed for the safe operation of IPT systems. FOD can be divided into system parameter detection methods, wave-based detection methods, and field-based detection methods. System parameter detection methods are normally used in low-power systems for MOD. Wave-based detection methods are suitable for high-power applications, for both MOD and LOD. Field-based detection methods work for both high-power and low-power applications, for both MOD (in an inductive way) and LOD (in a capacitive way). This tutorial first reviews and summarizes the state-of-theart development of FOD technology in IPT systems. Then, a novel detection coil layout is proposed to not only cover the whole charging area but also decouple from the transmitter and receiver to minimize the impacts on power transfer. A mixed resonant circuit will be explained which will have better performance than the parallel resonant circuit. The impacts of the detection coil layer, turn number, trace width, and the capacitance ratio in the mixed resonant circuit will be discussed.