Electric power grid applications impose many requirements on high-temperature superconductor (HTS) materials. In addition to a high superconductor transition temperature, these include all the parameters enabling a cost-effective, robust, and high-performance wire: high current-carrying capability in relevant ranges of field and temperature, flexibility and mechanical strength in a wire form, electrical and chemical stability, low ac loss, high wire uniformity, and low wire manufacturing cost with high reproducibility and yield. This daunting list explains why it has taken so long to bring HTS wires to where they are today—starting to be used in commercial power projects. The benefits of these wires are very significant: high efficiency and power density in an accessible temperature range, enabling high-capacity and easily installed cables, compact and powerful rotating machinery, and unique current-limiting functionality. However, the job is not done. Improved wire properties and reduced manufacturing costs of existing materials will further broaden the impact of this technology. Meanwhile the search for new materials—and for room-temperature superconductors—must continue, with more attention to thermal fluctuations, flux creep, and reduced anisotropy, which are critical to their application potential.