ChucK is a programming language for real-time sound synthesis and music creation. It is open-source and freely available on MacOS X, Windows, and Linux. ChucK presents a unique time-based, concurrent programming model that is precise and expressive (we call this strongly-timed), dynamic control rates, and the ability to add and modify code on-the-fly. In addition, ChucK supports MIDI, OpenSoundControl, HID device, and multi-channel audio. It is fun and easy to learn, and offers composers, researchers, and performers a powerful programming tool for building and experimenting with complex audio synthesis/analysis programs, and real-time interactive music.