Lithium depletion in the Universe remains a matter of investigation This book aims to carry out a wide-ranging inquisitive review of over half a century of astronomical observations of lithium and astrophysical developments to understand its behaviour in diverse environments across the Universe. The scope is wide, from the primordial nucleosynthesis in the early universe, to the evolution in the Milky Way and other galaxies and the internal processes that determine the depletion or preservation in stars, brown dwarfs and exoplanets.