This article is based on a longitudinal study of communication in a technical business environment. It describes a new medium of communication, the computer, comparing and contrasting the characteristics of this medium with those of more familiar media, such as pen-and-ink and face-to-face. The study focuses on the salient features of computer-mediated communication (CmC): the organization of conversation (opening, closing, and turn-taking); surface discourse features such as paralinguistic cues and simplification; choice of medium and medium-switching; and the acquisition of CmC. While certain modes of computer-mediated communication (CmC) share characteristics usually attributed to the oral mode, they also make use of characteristics of the written mode. Novices learn how to use CmC appropriately through strategies such as modeling. This enterprise provides us with another facet of ESP, the relationship between medium and language.