Unlike conventional radios, which are designed to work with specific waveforms (AM and FM, cellular, digital TV, and WiFi, for example), software defined radios can send and receive many different waveforms, and toggle between them on the fly by means of software code that defines their behavior at any particular moment. As such, they have the electronic guts and, increasingly, the artificial intelligence needed to navigate and even coordinate activity at the interface of the physical and digital domains. What is still needed, and what DARPA is aiming to energize, is a community of SDR users to map out and get comfortable within this fast-evolving landscape, and pave the way to a seamless and safe cyberphysical world.