Potential applications of high-temperature superconductors in electronics and communications are described with an emphasis on the relationship to the fundamental superconducting phenomena of zero resistance, magnetic-field expulsion and macroscopic quantum effects. The paper includes a description of the electric and magnetic properties of superconductors, potential microwave applications in filters, resonators, delay lines and superconducting transistors, and of mixers and other detectors. Simple logic circuits, an analogue-to-digital convertor and a SQUID magnetometer are also discussed, using the established conventional superconducting technology as reference point, and assessing the likely impact and importance of high-TCmaterials.