The American edition of this handbook contains concise informa­ tion on the basic physical properties of the elements and on their chem­ ical characteristics. In general, the data selected for inclusion in the handbook are those which either agree well with calculated data (in those cases where calculations could be carried out) or satisfy various correlations, particularly those based on concepts of the distribution of valence electrons of isolated atoms in the formation of a condensed state, as electrons localized at atomic ions in the form of energetically stable configurations, and as nonlocalized electrons. The Russian edition was published in the USSR in 1965, and new or previously omitted data have been added to all the sections of the present edition. In addition, the authors have considered it necessary to include a series of new sections. Thus, a new table has been included, "Electronic Configurations and Ground States of Free Atoms and Their Ions," since, in the ionization of some atoms (particularly for transition metals), the electrons are not always abstracted from the outer shell, and, consequently, calculation of the ground state (electron energy level) using the usual vector model does not give a direct result. The ground states are obtained experimentally and the table contains the corresponding data on the configurations and states of triply-ionized atoms (which is usually sufficient).