Twenty-eight specific communication media are defined and described in this monograph. A distinction is made between information and instruction and between instructional media and instructional aids. A set of criteria is proposed by means of which communication media may be distinguished from nonmedia, one medium may be distinguished from another, and a single medium may be distinguished from multimedia applications. A two-dimensional classification system for communication media is proposed. One dimension consists of seven media classes which are based on two ways of representing information--audio and visual. In the second dimension, communication media are divided into two groups, telemedia and recording media. The discussions and definitions are directed more toward media users, professional practitioners, and decision makers than toward scholars or research people. A glossary of standard media terms and phrases is provided. (Author/JY)