RF complexity in mobile phones continues to increase rapidly with the advent of 5G, making it even more difficult for phone manufacturers to meet stringent performance requirements. As phones include more antennas and support more frequency bands, it becomes increasingly challenging to maintain antenna performance across all usage conditions and frequencies. Impedance tuners help to solve the problem by maximizing RF power transfer under different conditions and across multiple frequency bands. As a result, they are increasingly being used to optimize performance, reduce design cost and meet 5G requirements. This white paper describes how impedance tuners can be used and discusses the relative advantages of different impedance tuner designs. It includes several examples that demonstrate how impedance tuning can be used to achieve significant performance improvements intypical real-world scenarios.