The principles and developments of experimental methods for determining the energy parameters governing the electronic structure of organic molecules and solids are reviewed with some historical descriptions. The energy parameters discussed are ionization energy of a molecule (I-g) and solid (I-s), electron affinity of a molecule (A(g)) and solid (A(s)), and the energies of the vacuum level (VL) and the Fermi level (E-F). The work function (Phi) can be also derived as the difference between the last two. Various types of spectroscopic and electrical measurements are discussed with typical examples, including the range of applicability and the merits and the demerits. Recent microscopic techniques for obtaining local information are also described.