In this book an attempt has been made to summarize the existing data on the hardness of elements and different compounds measured by various methods, and to assess their reliability. This assessment was based on measurements of the hardness of substances of different degrees of purity by various methods, taking into account the statistical factor when sufficient data were available for a statistical assessment. The data in this reference book are classified into the three following groups according to the electron configuration of the valence electrons in the individual elements: (1) elements with atoms that have s-electrons and completely empty or completely filled inner electron shells (alkali metals, beryllium, magnesium, alkaline-earth metals, metals of the Cu and Zn subgroups); (2) elements with atoms that have partially filled d- and f-electron shells (transition metals); and (3) elements with atoms that have valence sp electrons (nonmetals and semimetals). The different compounds were classified in the same groups.

Errata sheet inserted. Translated from Russian.