In wireless communication systems, In-phase and Quadrature (IQ) modulator and demodulator are usually used at transmitter (TX) and receiver (RX), respectively. For Digital-to-Analog Converter (DAC) and Analog-to-Digital Converter (ADC) limited systems, such as multi-giga-hertz bandwidth millimeter-wave systems, using analog modulator and demodulator is still a low power and low cost solution. In this kind of systems, the IQ imbalance cannot be ignored. Numerous papers have been published to investigate this problem. However, depending on different assumptions, different models of IQ imbalance are built and different approaches are proposed. This makes the researchers and system design engineers who are new to this topic difficult to start with. The goal of this book is to provide a unified IQ imbalance model and systematically review the existing estimation and compensation schemes. The intended audience of this book is the researchers who are interested in the IQ imbalance as well as the system design engineers who need to deal with the IQ imbalance in their systems.