The book discusses the main stages in the development of systems of units of physical quantities and gives an overview of the current state of the issue of units of measurement and systems of units. It presents the results of international work on units of measurement, provides a critical analysis of different systems of units and reviews the International System of Units adopted at the Eleventh General Conference on Weights and Measures. The issues of standardization of units of measurement in the USSR are widely covered, the main provisions and tables of State standards for units of measurement are given. Reference materials on units of measurement are also placed in the book.