Role of lightning data in understanding Terrestrial Gamma-Ray Flashes (TGFs)

New data from NASA's Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite have revitalized the study of Terrestrial Gamma-Ray Flashes (TGFs), brief (1ms) flashes of gamma rays observed from low-Earth orbit over thunderstorms. One of the most important advantages of the new TGF observations has been the ability to correlate them with radio atmospherics from lightning observed by a number of groups. I will discuss the status of TGF observations, the open questions about the physics of their origin and their association with other phenomena, and the role of radio and optical observations of lightning in solving the TGF mystery.