The goal of this paper is to aid both clinicians and developers in understanding the issues associated with alternative input systems that permit full access to the IBM-PC family of computers. The first part of the paper discusses the concept of keyboard emulation in general and reviews a variety of keyboard-emulation systems that are currently available. The capabilities of a system called ALTKEY, developed in our laboratory, are described. The second part of the paper discusses the implementation of a keyboard-emulation system in more detail, using ALTKEY as a specific example. Technical design issues are discussed, and successful approaches to these design challenges are presented.