When asked about the purpose of human language, most people would instinctively reply that its main purpose is communication. Most of us take for granted our ability to communicate easily through language. It would be natural for us, as computer users, to expect the same degree of ease when we interact with systems and user manuals. But even computer professionals and other experienced users are often baffled by the explanations that appear in so-called “help” facilities; perplexed by the meanings of words in menu options, on toolbars, and buttons; and hampered in information retrieval by having to use terms that do not readily express their needs. Words on the computer screen can create a barrier to communication, yet users who turn to help files or documentation are frequently disappointed. Times columnist Lynne Truss speaks for many when, at the end of yet another unrewarding session on her computer, she declared: “I have even stopped looking at those files titled ‘Read This,’ because it’s sad but true; I have never yet opened one whose contents I could understand” (1996). Often, a frustrated cry of “I don’t understand the options on the screen” leads many users to just “try it and see what happens,” with potentially disastrous or time-wasting consequences. “I don’t understand the manuals” is another typical refrain, which provides an excellent reason for not reading them. It has been said so often (e.g., Smith 1992), that alternative ways of informing or teaching users are now being promoted; for instance, video training. This mode of delivery can make information more palatable, but it does not eliminate the problems created by confusing use of language in the user interface. The difficulties experienced by both professional and casual or new users are not inevitable; they are not something to be accepted as a feature of computer systems, manuals, and on-line documentation. Something can be done to improve the way that language is presented and used in these contexts. This book provides the necessary communicative framework as well as practical recommendations to make it possible to significantly improve user interface and documentation design.