In recent years, interest in the problems of physical-geographical regionalization has increased sharply among Soviet physical geographers. This interest is by no means accidental. The study of regional differences in natural conditions across the vast and diverse territory of our country, and the identification of integrated physical-geographical complexes possessing distinctive and orderly structures (which differ both in their natural resources and in the conditions for their development), constitute perhaps one of the most important scientific and practical tasks of physical geography. A scientifically grounded regionalization scheme developed on the basis of sound logical principles is one of the most rational forms for synthesizing the results of regional geographical research. According to the currently accepted view, physical-geographical regionalization marks the completion of a particular stage in the study of a given territory. At the same time, regionalization represents one of the forms of geographical research output that is most readily understood and applied by a wide range of practitioners. It is entirely natural that an understanding of the specific character of geographical differences and the regularities governing the spatial distribution of physical-geographical complexes is especially important for countries of great territorial extent, where geographical contrasts are particularly pronounced and exert a strong influence on the characteristics of economic activity and the location of various sectors of the economy. For this reason, it is not surprising that Russian geographers have devoted more attention to questions of regionalization and have pursued them more thoroughly, effectively, and seriously than their foreign counterparts. Over a period of one and a half centuries, the idea of regionalization has run like a continuous thread through many classic works of Russian geography, gradually becoming more refined and mature. B. A. Variskaya was entirely correct in this regard when she wrote (Problems of Geography, Vol. 17, 1950, p. 139): “The history of our geography is to a considerable extent the history of its regionalization.” This collection is primarily devoted to a review of published materials on the physical-geographical regionalization of the territory of the Soviet Union up to 1956. The significance of such a review lies in its ability to assess the current state of research concerning the natural differentiation of the country's major regions, while at the same time clarifying the principal problems of physical-geographical regionalization and identifying tasks requiring solution in the near future. This work is particularly relevant at present because geographical research groups in most Soviet universities are actively engaged in extensive studies of physical-geographical regionalization in support of long-range agricultural planning. The collection reviews materials relating to the following major regions of the Soviet Union: the Russian Plain, the Urals, Siberia, Kazakhstan, Central Asia, the Caucasus, and the Far East. These regions also form the subject matter of the principal articles included in the volume. Most contributions describe and analyze materials concerning both integrated physical-geographical regionalization and branch (sectoral) forms of natural regionalization, including tectonic, geomorphological, climatic, hydrological, soil, phytogeographical, and zoogeographical classifications. The articles review works dealing with entire regions as well as selected studies devoted to particular areas, especially those that are of major importance, possess special significance, or are representative in character. The only exceptions are the articles by N. A. Solntsev on the Russian Plain and M. A. Glazovskaya on Kazakhstan, which examine only integrated physical-geographical regionalization schemes and focus primarily on those covering the major Soviet regions listed above. The editors consider that, in N. A. Solntsev’s article, the final two sections do not present the issues under discussion with sufficient objectivity and are, in many respects, highly controversial. Nevertheless, the editors deemed it necessary to publish the article in its entirety and preserve its integrity, in order to facilitate further discussion of N. A. Solntsev’s views concerning the regionalization of the Russian Plain. The volume concludes with several short articles and reviews directly related to problems of physical-geographical regionalization in the Soviet Union. Owing to technical considerations, some map illustrations are placed at the end of the book (see inserted plates).