Recognition of the consequences of the creation of collective excitations (e.g., plasmons) of the valence electrons in a solid by "low-energy," i.e., 50-500 eV, electrons led to a reformulation of the theory of electron solid scattering, the use of electron spectroscopies for surface characterization, the rise of surface science as a recognized interdisciplinary research area, and the emergence of the American Vacuum Society as a major international scientific society. These transformations occurred between 1968 and 1973. This recognition and the concomitant advances in electron-solid scattering theory were extended to positron-solid scattering during the following decade. By virtue of these developments, low-energy electron and positron diffraction became the techniques of choice for determining the detailed geometries of the top few atomic layers of single-crystal solid surfaces. (C) 2003 American Vacuum Society.