Ultraviolent (UV) radiation represents a comparatively small part of the total electromagnetic spectrum, yet this portion of the spectrum is responsible for an extremely wide range of effects in many different settings. In biological systems, it can produce good and bad outcomes. We use UV radiation to drive chemical reactions that are desired, and we know that it also drives environmental reactions that are harmful to living organisms. We use UV radiation to interrogate molecules and to analyze cells. Some animals view our world in the UV radiation range, while astronomers use UV to study the universe; in both cases, what is observed is very different from that observed using other parts of the electromagnetic spectrum. This volume gives the reader just the very beginning of the broad range of properties, applications, and effects of UV radiation and is intended to stimulate the reader to explore more of this fascinating part of the electromagnetic spectrum.