Planck's half-quanta: A history of the concept of zero-point energy

Max Planck introduced the concept of zero-point energy in spring 1911. In t he early struggles to establish the concept of the energy-quantum, it provi ded a helpful heuristic principle, to guide as well as supplement the effor ts of some leading physicists ill understanding the laws that applied in th e atomic domain. The history and growth of this this concept, and its appli cation in the general development of quantum theory during the past many de cades are studied under three principal headings: (I) The Birth of the Conc ept of zero-Point Energy; (2) Does Zero-Point Energy Really Exist? and (3) The Ground Stale of Quantum Systems.