This chapter gives an overview of the technology and design of radiofrequency (RF)‐integrated circuits in silicon technology. These circuits have transformed the field of wireless communications, forming the heart of sophisticated multiple‐input, multiple‐output RF transceivers for use in cellular handsets. The technology is now starting to transform new fields in the millimeter‐wave frequency range, enabling it to be used for new consumer applications such as radars for autonomous cars. The chapter describes the key active device technologies and passive components before going on to describe the state of the art in circuit design techniques. There are separate sections dedicated to the design of amplifiers, oscillators, mixers and modulators, and integrated transceivers. A final section gives an introduction to the importance of taking the packaging into account at the chip design and layout stage, as well as describing the rapidly emerging field of RF system‐in‐package technology, where sophisticated millimeter‐wave antenna arrays can be integrated with active circuits. The chapter includes 180 references to research papers describing advanced techniques developed in both industry and academia.