Electronic instruments encompass everything from wired versions of traditional instruments like electric guitars to fully digital systems for live performance. Many are hybrid combinations comprising mechanical, electronic and software components. This chapter focuses on digital music instruments (DMI’s) and will be best appreciated with some familiarity having been gained by playing digital keyboards, drums or other DMI’s. To a designer of these kinds of instruments, everything is a signal. As we step through the layers involved, I’ll describe processes for sensing, transduction, signal processing, and sound generation. The discussion wraps up with some new technologies using mobile devices and web browsers as instruments and DMI designs replicating earlier analog electronic instruments.