Urban agglomerations are being formed and developed on all continents and demonstrate various development scenarios and educational models. The concept of agglomeration is considered, and a list of Russian and foreign authors who have made a significant contribution to the study of the phenomenon of agglomeration is presented. The description and analysis of various models of urban agglomerations development are presented. The reasons for the appearance of urban agglomerations, approaches and patterns, advantages and negative sides of this process are investigated, and the peculiarities of the formation of urban agglomerations and agglomerated territories in Russia and abroad are studied. The criteria for recognizing territories as urban agglomerations are listed. It is noted that the level of development of the center is crucial for the development of adjacent territories. Examples of agglomerations in Europe, North America, Latin America, Japan and Russia are considered. Examples of the largest agglomerations are given. The features of spatial development and formation of agglomerations in the Russian Federation, largely due to the large area of the territory, are presented. It is concluded that it is necessary to form a supporting framework based on the development of regional centers and subcentres. The process of formation of the Astrakhan agglomeration as a regional center is investigated, and ways of its further development are proposed. Some provisions of the “Spatial Development Strategy of the Russian Federation for the period up to 2025ˮ and the regional law “On the development of Agglomerations in the Astrakhan region” are considered, which confirm that the system of spatial and territorial development of the Astrakhan region is still at the stage of formation.