The main focus of this paper has been to determine the functional regions in the heterogeneous area of Slovenia defined by integrated urban system at the (inter)national level. The notion of polycentric urban development is taken from the local and regional perspective based on the principle of proximity where cooperation, exchanges and networks among cities can contribute to the development of integrated urban systems to overcome the legacy of the inherited urban structures. Delineation of Slovenia into functional regions is based on labour market approach, where daily labour commuting has been considered as the main factor, which determines connectivity/relation between predefined local urban centres and municipalities in the functional regions. The urban centres of national and international importance in Slovenia have been determined mainly according to the number of inhabitants and their role in the polycentric urban system of Slovenia according to the Spatial Development Strategy of Slovenia (SPRS 2004).