This volume gives a comprehensive overview of current knowledge about the light nuclei created in the Hot Early Universe: H, D, 3He, 4He, and 7Li. It combines observational and theoretical results on the early Universe, the distant galaxies, our Milky Way, the local interstellar cloud, and the solar nebula. The implications for cosmology, galactic and stellar evolution, dark matter research etc. are outlined and directions of future research are indicated.