Telephone eavesdropping devices, radio transmitters, passive and active listening devices, audio system accessories, and sophisticated eavesdropping techniques are reviewed. Countersurveillance radio receivers; telephone analysis equipment; electronic aids to physical inspection; and protection devices, such as acoustic rooms, disconnect devices, filters, and various radio jammers, are described. Attention is focused on computer security and eavesdropping on information processing machines. Night viewing devices and systems and various tracking devices such as beacons and radio navigation systems are considered. Additionally, potential developments within the audio and visual surveillance technologies are projected. The use of tape recordings as evidence in court proceedings is addressed, and requirements for admissibility of tapes into evidence are delineated. Signs suggestive of falsification are highlighted and are classified as gaps, transients, fades, and extraneous voices. Types of tape falsification are noted, and an analytical approach to the detection of falsification is suggested. Two hypothetical cases illustrating the application of the analytical approach are included; problems identified in the practical application of this approach are scarcity of factual information, restrictions on measurement, availability of analysis equipment, competence of the forensic examiner, and time and cost. Finally, two actual cases that illustrate a variety of problems are provided. Specific short- and long-term solutions to the problems of forensic examination of tapes are offered. Eighteen illustrations, 4 tables, 2 glossaries, and approximately 75 references are included.