This standard is a revision of ANSI S3.2-1989 (R 1999) American National Standard Method for Measuring the Intelligibility of Speech over Communication Systems. The standard provides three alternative sets of lists of English words to be spoken by trained talkers over the speech communication system to be evaluated. The selection of the particular set of word lists depends upon the purpose and constraints of the test situation. Trained listeners record the words they hear. The fraction of the words they identify correctly is the measure of the intelligibility of speech over the system. The system may consist of the air and the room or outdoors in face-to-face communications; the equipment and environments used in telephony, public address systems, or ordinary radio; or complex systems of environment, equipment, and air, wire, fiber, radio, and water paths used in some military, space, remote, or emergency communications. The standard specifies test materials that have been thoroughly validated. The standard also specifies methods for selecting and training the talkers and listeners; for designing, controlling, and reporting the test conditions; and for analyzing and reporting the test results.