This article is a comprehensive study of organized criminal groups (OCGs) in the modern world, covering the theoretical foundations of their study, structural characteristics and functional aspects of their activities. The paper traces the evolution of the concept of organized crime in criminological science, analyzes modern approaches to the definition and classification of OCGs, and considers the legal aspects of their definition at the international and national levels. Special attention is paid to the analysis of the structural characteristics of modern organized crime groups, including traditional hierarchical models, network structures, hybrid forms of organization, as well as new forms such as cluster and project organization. The study shows a trend away from rigid hierarchical structures towards more flexible and adaptive forms of organization, which allows OCGs to effectively resist law enforcement pressure and adapt to changing conditions. The article also examines key functional aspects of organized crime groups, including their role in the shadow economy, establishment of corruption links, transnational activities, use of modern technologies and adaptation to countermeasures. The impact of globalization and technological progress on the evolution of OCG forms and methods of operation is highlighted. The study demonstrates the need for an interdisciplinary approach to the study of organized crime, taking into account the complexity and dynamism of this phenomenon. The work contributes to the understanding of current trends in the development of organized crime and can serve as a basis for the development of effective strategies to counter organized crime.