A-Shell BASIC, frequently referred to in this documentation as "ASB," is the primary programming language used for developing applications in A-Shell. A super set of the original BASIC, which was introduced in 1976, it shares many features with other BASIC-like languages, while adding a number of features particularly useful for developing vertical market applications in Windows and UNIX environments. These include a mechanism for precise memory layout of structures (MAP statements), various integrated, cross-platform, file access methods, and the ability to call external routines written in C or ASB. It is partially compiled to p-code, which is then executed within the A-Shell runtime environment.

Because most of the users of ASB are already familiar with earlier versions of BASIC, documentation for the common features has not been a priority. But over time, as new programmers come into contact with ASB who are not familiar with its predecessor, the need for a more complete reference to the language has become more pressing. The following sections attempt to provide the necessary details so that both newcomers and long-time A-Shell developers can get the most out of ASB.