The problem of developing a unified general classification of landslides has not lost its relevance; on the contrary, it has become even more acute and practically important today. However, the creation of such a unified classification faces considerable difficulties. There is still no consensus regarding the purpose of such a classification, the appropriate number of classifications, or the characteristics that should serve as the basis for classification. At the same time, both in our country and abroad, the number of landslide classifications constructed according to different principles, often in violation of the rules of logic, continues to increase unreasonably. All of this provides grounds for speaking of a certain “classification boom,” which, rather than simplifying matters, has significantly increased the difficulties faced by geological practitioners. Evidence of this unsatisfactory situation in the important field of engineering geological dynamics was reflected in the collective monograph Problems of the Classification of Gravitational Slope Processes, published by Nauka Publishers in 1986 and prepared by leading domestic experts in landslide studies. Yet even in this comprehensive work, no common platform was established on the most fundamental questions of landslide classification. Against this background, the monograph by N. F. Petrov, devoted to the classification of complex landslides viewed as landslide systems, will undoubtedly attract the attention of specialists engaged in the study of natural and engineering geological processes. The book develops many of the ideas previously presented by the author in his earlier work, Landslide Systems: Simple Landslides (A Classification Perspective) (Shtiintsa Publishing House, 1987). In both of these books, the author seeks to analyze comprehensively the extensive accumulated material on landslide classification from a systems-theory perspective while skillfully drawing upon the valuable experience of systematic taxonomy developed in biology and in such earth sciences as stratigraphy, paleontology, and paleobotany. Thus, Petrov's book cannot be regarded as an ordinary event in theoretical landslide science. Its publication marks a new stage in the development of this field, which is especially important given the scarcity of major publications on the subject in recent years. Complex landslides, considered as landslide systems, are widespread in nature, yet they have received little study. The book focuses primarily on the structural aspect of landslides, in the geological sense, which remains one of the least developed areas of research. Basic concepts are clearly defined, and four principal hierarchical levels are distinguished: the block level, the layer-band level, the terrace-segment level, and the multi-terrace-segment level. The last two levels are formally identified and defined for the first time. A substantial portion of the book is devoted to the systematization of the characteristics of complex landslides. The structure of landslide bodies and the components of landslide-system structure are clarified. Particular attention is given to blocks as the basic units of landslide bodies, and their functional roles are identified. Structural elements belonging to other hierarchical levels are examined with equal thoroughness. Previously accumulated knowledge is critically reassessed, and, on this basis, models are constructed that contribute to a deeper understanding of the mechanisms and dynamics of landslide processes. The principal result of the study is the development of a classification of landslide body-systems. Although some details of the classification may require substantial revision, this in no way diminishes the author's achievement. He has accomplished the difficult task of integrating a vast body of heterogeneous material scattered throughout numerous publications into a unified and, in our view, internally consistent system. In the concluding section of the monograph, the requirements for establishing a universal natural classification of landslide systems are formulated. Based on a critical analysis of the views of leading specialists in the field, the author proposes a number of constructive suggestions. At the same time, he presents his own views on landslide mechanisms, which serve as the objects of classification in the form of kinematic models. In recent years, this position has gained understanding and support from many leading researchers and will undoubtedly contribute to the further development of landslide science. Although one may fully agree with many of the ideas and viewpoints expressed by Petrov, it is impossible to remain silent regarding certain controversial positions and unresolved questions. For example, the concepts of “terrace segment” and “multi-terrace-segment landslide” appear insufficiently developed. The author frequently departs from his own definitions of these concepts; in some cases, their scope becomes ambiguous, and the boundaries between individual terrace segments remain rather vague. Furthermore, the combination of the term “terrace segment” with the terms “layer band” and “block” is itself not entirely successful. When constructing a landslide classification, insufficient attention is paid to the composition, state, and properties of the material forming the landslide body, that is, to its material characteristics. These characteristics often appear implicitly and are classified by the author as environmental features, a position with which we cannot agree. In our view, it is impossible to represent landslide mechanisms solely on the basis of geometric, kinematic, and genetic characteristics. The deformation and rheological behavior of the material constituting the landslide body are primary factors determining the nature of landslide mechanisms. Consequently, they should not be excluded from the characteristics of the landslide itself and relegated to environmental attributes. Otherwise, it becomes impossible to distinguish many categories of landslides according to their mechanisms, including all categories of “special landslides.” The monograph does not substantially address landslide dynamics, historical genesis, or several other aspects of the problem. Among these, the dynamic aspect is particularly important to the topic under discussion. As is well known, geological bodies undergo significant changes during the development of landslide processes, and these changes affect all hierarchical levels. Clearly, the static consideration of inherently dynamic landslide systems is merely a methodological device appropriate to the current stage of research. The author himself fully recognizes this and identifies the study of landslide dynamics as one of the primary tasks for future investigations. Such studies may eventually make it possible to examine the spatial and temporal variability of landslide mechanisms and the evolution of landslide systems under different engineering-geological conditions. It would not be difficult to point out other shortcomings and inaccuracies in the work. Certain sections are highly controversial and may, in some respects, be overly generalized. Nevertheless, this should also be regarded as one of the monograph's strengths, since it stimulates thought, challenges established paradigms, and, most importantly, directs researchers' attention toward both unresolved and newly emerging problems. This will undoubtedly have a positive impact on strengthening landslide theory and advancing engineering geological dynamics as a whole. Such, indeed, is the principal purpose of Petrov's book. There can be little doubt that this monograph will become a valuable methodological guide for specialists engaged in the study, prediction, and engineering mitigation of landslides and other geological processes, as well as for those concerned with nature conservation and the rational use of the geological environment.