This book focuses on high performance radio frequency integrated circuits (RF IC) design in CMOS. 1. Development of radio frequency ICs Wireless communications has been advancing rapidly in the past two decades. Many high performance systems have been developed, such as cellular systems (AMPS, GSM, TDMA, CDMA, W-CDMA, etc. ), GPS system (global po- tioning system) and WLAN (wireless local area network) systems. The rapid growth of VLSI technology in both digital circuits and analog circuits provides benefits for wireless communication systems. Twenty years ago not many p- ple could imagine millions of transistors in a single chip or a complete radio for size of a penny. Now not only complete radios have been put in a single chip, but also more and more functions have been realized by a single chip and at a much lower price. A radio transmits and receives electro-magnetic signals through the air. The signals are usually transmitted on high frequency carriers. For example, a t- ical voice signal requires only 30 Kilohertz bandwidth. When it is transmitted by a FM radio station, it is often carried by a frequency in the range of tens of megahertz to hundreds of megahertz. Usually a radio is categorized by its carrier frequency, such as 900 MHz radio or 5 GHz radio. In general, the higher the carrier frequency, the better the directivity, but the more difficult the radio design.