Open-source technologies have created new expressive opportunities by expanding the creative music palette into the realm of circuits and source code, democratizing the line between design and creative application. Sound & Music Projects for Eurorack & Beyond explores the intersection of music, computer science, and electronics in the context of Eurorack, a popular framework for mounting and interconnecting modular synthesizers. This book provides a practical path for musicians and other artists to envision and build custom electronic instruments using freely available software and a modest collection of tools and electronic components. Hands-on projects are based on Teensy microcontrollers, a category of USB-based devices that are easy to program for a variety of music and sound-design applications including music synthesis, digital signal processing, and the Musical Instrument Digital Interface. Mini projects include a genetic step sequencer, interactive arpeggiator, custom effects unit, and synthesizers based on several typologies including frequency modulation, subtractive, additive, and granular synthesis. Sound & Music Projects for Eurorack & Beyond is comprised of four sections that explore music synthesis and digital signal processing, the Musical Instrument Digital Interface, Eurorack concepts, and Eurorack projects. The text culminates with several custom Eurorack modules including an audio mixer, audio effects unit, MIDI to control-voltage converter and Eurorack synthesizer. Throughout the book, readers will develop relevant skills including microcontroller programming, circuit design, PCB design, and instrument fabrication in a building-block fashion that fosters experimentation and creative application.