The interior of an explosion is one of the harshest environments on earth. The violent chemical reactions and rapid changes in pressure and temperature make sensing with conventional electronics virtually impossible. One can obtain signi†cant information using remote optical techniques, and indeed the spectroscopy of explosions is a major †eld of research [1,2]; however, the presence of debris or opaque chemical reactions can make the †reball impossible to probe, even with the most advanced equipment. In this chapter, we describe temperature and thermal history sensors based on microparticle or nanoparticle luminescence. These particles are embedded in explosive material and disperse with it but are undamaged by the explosion since they have no mechanical or electronic “parts.” The luminescence of the particles can be examined in the debris or measured in a laboratory and can ascertain the.