A review of the history, design, performance, and application of electret transducers is presented. Particular emphasis is placed on foil‐electret transducers incorporating a thin‐film electret made of Teflon or related materials. Such transducers have excellent frequency response, low distortion, small vibration sensitivity, and have been used over a frequency range extending from 10−3 to 2 × 108 Hz. They can be made in a variety of shapes over a large range of sizes and are generally not affected by adverse environmental conditions. More than 10 million electret transducers are being manufactured annually as microphones with various directivity patterns for use in amateur and studio applications, tape recorders, sound‐measuring instruments, telephone‐operators' headsets, hearing aids, and acoustic‐graphic tablets, and as transducers in earphones and phonograph cartridges. Electret transducers are also used for experimental and research applications in such widely different fields as gas analysis, opto‐acoustic spectroscopy, aeronautics, atmospheric studies, telephony, ultrasonics, acoustic holography, data transmission, and leak detection in space stations.