Biophotonic Therapy uses light in an extracorporeal or intravenous mode to activate the red blood cells, a form of immunity inherited from humankind’s distant oligocellular ancestors. BT has an instructive 100-year history; a range of modalities; well-characterized mechanisms of action; a wide array of indications; several counterindications; well-understood, limited side-effects in certain cases; and a scientific literature that now includes more than 400 articles as well as a score of books. No drug resistance to BT has ever been reported.