Reports of gamma rays and neutrons observed at ground level below thunderstorms have appeared in the scientific literature for the past several decades. There have also been observations of intense flashes of gamma rays and electrons associated with thunderstorms by at least four different orbiting spacecraft since 1994. These have been termed terrestrial gamma ray flashes (TGFs). The latest development in this area of research is a comprehensive set of ground-level measurements of the spectra of high-energy gamma rays and electrons, along with neutrons, from a large array of cosmic ray detectors on Mount Aragats, in Armenia. The relationship of ground-level radiation to spaceborne TGFs is unknown, and details of the origin of both phenomena are still highly uncertain.