Fluorescent Nuclear Track Detector technology is a passive luminescent integrating detector technology having important advantages in measuring neutrons, heavy ions and even photons. FNTD is based on new aluminum oxide crystals doped with carbon and magnesium impurities (Al₂O₃:C,Mg) and confocal laser scanning fluorescent microscopy technique. The production and optical characteristics of Mg-doped aluminum oxide are discussed in details, as well as the progress made in the read-out instrumentation. Since the introduction of the technology, FNTDs have been successfully used for a wide range of applications in mixed neutron-gamma fields, medical dosimetry and radiobiological research and the results of these tests are discussed in detail.