Advances in computer design and applications have brought about an increased use of electronic transmission systems for conveying information. Discussed in this paper are the components of the system (terminals, channels, multiplexor, computers). Data communications applications are of two major types - intraplant and interplant. Examples of the former are data collection, quality control, assembly line broadcase, process control, and conversation programming. Examples of interplant communications are order entry, scheduling, and remote job processing. Each of these applications is discussed in detail.