Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, and is represented by the symbol He. It is a colourless, odourless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among the elements and it exists only as a gas except in extreme conditions. Next to hydrogen, it is the second most abundant element in the universe, and accounts for 24 per cent of the elemental mass of our galaxy. This book presents current research data in the study of helium, including helium in the terrestrial upper atmosphere; an experimental and analytical investigation of helium in metals diffusion; the release of mantle helium and its tectonic implications; and, the study of helium behavior in nuclear fuel materials.