APL is a high-productivity computing tool which is concise, has a consistent mathematical foundation, is intrinsically an array processing language, and has been developed over a period of more than 30 years. It is distinguished by its simple and consistent rules, a large set of built-in capabilities, powerful facilities for defining new operations, and a general and systematic treatment of arrays. Major APL users include financial institutions, insurance companies, engineers, scientists, mathematicians and teachers. Applications for which it is used range from pure mathematics through engineering calculations and on to free-form text retrieval.