Software radio is a set of technologies for defining radio transceiver parameters and functions in software, including carrier frequency, modulation bandwidth, channel coding, and frequency/space/time/code agility. In previous generations of telecommunications systems, these parameters and functions were sometimes selectable but generally were hardware‐defined, with software programmability limited to baseband digital signal processing. This chapter provides an overview of the software radio technology and applications ranging from the ideal software radio through practical designs to the broader implications, especially for radio spectrum management.