Limbo is the application programming language for the Inferno operating system. Although Limbo looks syntactically like C, it has a number of features that make it easier to use, safer and more suited to the heterogeneous, networked Inferno environment: a rich set of basic types, strong typing, garbage collection, concurrency, communications, and modules. Limbo may be interpreted or compiled 'just in time' for efficient, portable execution. This paper introduces the language by studying an example of a complete, useful Limbo program. The program illustrates general programming as well as aspects of concurrency, graphics, module loading, and other features of Limbo and Inferno.