XL-Calibur is a collaboration amongst scientists from the United States, Japan, and Sweden, led by the Principal Investigator, Henric Krawczynski from Washington University (St. Louis). The mirror uses a flight spare from the Hitomi mission, a gondola and pointing control mechanism developed at NASA’s Wallops Space Flight Center, and a fully active shield developed at KTH in Sweden. The mission is flown on Long Duration Balloon (LDB) flights launched from McMurdo (Antarctic) or Jukkasjärvi (Sweden) as part of NASA’s Scientific Ballooning program.