A mixer is an indispensable device in the RF transceiver system. Along with the rapid development of mobile communication technology, the demand on the RF mixer for compatibility with multiple communication standards and functional diversity is increasing. As a result, the mixer with wider bandwidth, lower noise, higher linearity, and less power consumption is urgently needed. In the article, the basic principle and the circuit architectures of the mixer are reviewed, including the essential performances such as linearity, noise, gain, bandwidth, and so forth. In addition, several aspects are presented, compared, and discussed with particular emphasis on optimization design approach and performance. Current design and fabrication challenges, future development, application areas of the mixer and visions for the mixer are also discussed in this review.