The principles underlying the identification of the various classes of diurnal conditions were examined. The key unit in the classification is the type of diurnal condition, determined by the relationship between the thermal interval, the gradation of moisture levels, and the change they cause in the vertical structure of the natural territorial complexes. Sixty-six types and sub-types of diurnal conditions were identified on the basis of data obtained by semi-stationary and expeditionary research. -translated by P.Cooke