Helium is the second most abundant element in the solar system after the hydrogen atom and also the simplest of all atoms. In this book the authors present topical research in the study of the occurrence, applications and biological effects of helium. Topics discussed include the discontinuous yielding, stress drops and strength of metals in liquid helium; the use of helium with oxygen at pressure as a breathing gas mixture; the physics and chemistry of helium clusters and droplets; the interaction of helium atoms and ions with matter; postseismic leakage of mantle and crustal helium from seismically active regions; weak superfluidity of the nonstationary Josephson effect in He-4 and possible applications; and clean energy from Helium-3 fuelled muon-catalysed aneutronic fusion.