The aim of this work is to present the conditions for the development of Tri-City as the main metropolitan centre of northern Poland. The article is also an attempt to evaluate the current process of cooperation and conflicts between metropolitan cities and the possibility of introducing a metropolitan union in Tri-City. Tri-City has been presented against the background of the main urban centres in the country and the area has been subjected to the delimitation test. Successes in the field of joint investment projects of cities were presented. Criticisms have been made of the existing integration forms of communes established in the metropolitan area. The conducted analysis confirmed strong integration processes and the possibility of introducing a Metropolitan Union in Tri-City as modelled on Górnośląsko-Zagłębiowska Metropolia (GZM). This paper presents a research method – a case study, in which comparative analysis was used. Quantitative and qualitative description methods, statistical data, and analysis of documents regarding integration initiatives have been applied.