This paper discusses the design and building of an APL interpreter for the IBM Personal Computer. Discussed is the writing of the interpreter itself, which required the use of an intermediate language designed by the authors. This machine-independent language also made possible the development of APL interpreters for two other systems-stem/370 and Series/1. The particularizing of the interpreter required a compiler, which in the case of the Personal Computer produced Intel 8088 and 8087 assembly language code. The matching of the APL interpreter to the operating system (DOS) required an APL supervisor, which is also discussed in this paper. The provision of the APL character set presented problems, the solutions of which are also presented. Other topics discussed are the display, the keyboard, and the session manager.