Biophotons are photons within or emitted from living organisms. Biophoton emission (ultraweak photon emission) is now accepted as a universal phenomenon, involving weak light emission from a few up to several hundred photons / s·cm2. Biophoton emission originates from a non-localized coherent electromagnetic field within the living body and is regulated by the field. In this paper an account is given of the coherent properties of biophotons and their functions in cell communication and therefore in biological regulation, based on experimental results concerning the non-linearity of biophoton emission, the hyperbolic decay of reemission after illumination, and the Poisson and sub-Poisson distributions of photocount statistics. From the point of view of the interactions between biological structures and biophoton fields some discussions on the origin of biophotons and their impact are presented.