The article notes that the territorial organization of local self-government in Russia determines the need for horizontal interaction or inter-municipal cooperation. At the same time, it is proved that the implementation of various forms and types of inter-municipal cooperation cannot be assessed as sustainably effective, some gaps in the legal regulation of the status of associative inter-municipal associations are noted. The author substantiates the urban or urbanized nature of the absolute majority of unions and associations of municipalities. The individual advantages and disadvantages of agglomerations are evaluated. The assumption is made that the fundamental basis of inter-municipal cooperation is the legal personality of its participants and the corresponding conclusions are formulated about the importance of inter-municipal cooperation for the transformation of the territorial basis of local self-government.