Аннотация:“Ultraweak photon emission (UPE),” “biophoton emission,” “biological autoluminescence (BAL),” “biochemiluminescence (BCL),” etc. are different terms for the phenomenon of intrinsic (spontaneous) photon emission of extremely low intensity, which is characteristic of all biological systems as well as many model objects. The system composition, its state, and external conditions determine its intensity, spectrum, and, possibly, other physical properties, but the phenomenon itself remains universal. This brief introduction outlines the main historical milestones and basic concepts in the field of ultraweak luminescence. A detailed presentation of these issues will be given in the later parts of the book.