Although electron energy spectra have been studied for years, only more recently has their usefulness in chemical‐structure problems been appreciated. Now we appear to have a new analytic method that can describe the complete electronic structure of a molecule by measuring binding energies for all the orbitals. Optical spectroscopy, in comparison, measures only the first ionization potentials, except for the very simplest molecules. And electron emission spectra, we shall see, are also useful in such applied work as protein structure analysis and investigations of environmental pollutants.