Defining Pathways for Realizing the Revolutionary Potential of High Entropy Alloys Scientific exploration in the field of high entropy alloys, known as HEAs, has recently exploded. First reported in about 2004, HEAs were defined originally as a blend of five or more elements with concentrations between 5 to 35 atom percent, and with a strong preference towards single-phase, solid solution metallic alloys. Later, the field branched to include intermetallic and ceramic compounds, alloys with as few as three principle elements, and microstructures with any number and type of phases. Today, researchers face vast combinations of elements with which to work, and they eagerly seek to learn more about HEA compositions, microstructures, promising property combinations, and opportunities for a wide variety of applications in both structural and functional materials. HEA development offers tremendous potential not only for expanding scientific knowledge, but also for creating a broad range of revolutionary products for strategic, economic, and national security benefits.