Frequency dividers are important circuits in fully-integrated radio-frequency circuits. This book introduces the design of wide locking range injection-locked frequency dividers(ILFDs) using multi-resonance RLC resonator. An ILFD using single-resonance LC resonator has one locking range. An ILFD using multi-resonance LC resonator has multiple locking ranges, which are overlapped to emulate a single locking range. Many practical examples using LC resonators and RLC resonators are used to demonstrate the usefulness of the design method.