A15 refers to a cubic crystal type in the Strukturbericht System represented by the example Cr3Si. The intermetallic A3B compound is formed by a body-centered cubic (bcc) arrangement of B atoms with two A atoms centered in every face yielding orthogonal chain structures running through the crystal. The A atoms are from the groups IVA, VA, and VIA transition metals, whereas the B atoms are from groups IIIB, IVB, and VB and some transition metals including osmium, iridium, platinum, gold, and technetium. This article reviews the phase diagrams and provides information on alloying, critical current density, and properties of A15 superconductors. It describes the assembly techniques for tape conductors and multifilamentary wires. The article discusses the applications of A15 superconductors in commercial magnets, power generation, power transmission, high-energy physics, and fusion.