ChucK is a programming language designed for computer music. It aims to be expressive and straightforward to read and write with respect to time and concurrency, and to provide a platform for precise audio synthesis and analysis and for rapid experimentation in computer music. In particular, ChucK defines the notion of a strongly timed audio programming language, comprising a versatile time-based programming model that allows programmers to flexibly and precisely control the flow of time in code and use the keyword now as a time-aware control construct, and gives programmers the ability to use the timing mechanism to realize sample-accurate concurrent programming. Several case studies are presented that illustrate the workings, properties, and personality of the language. We also discuss applications of ChucK in laptop orchestras, computer music pedagogy, and mobile music instruments. Properties and affordances of the language and its future directions are outlined.