When analysing the nature of intergovernmental relations in Poland, it is important to consider historical, political, and territorial factors. Poland is a territorially large country in Central and Eastern Europe. It is a unitary state without autonomous regions and is deeply decentralised, with three levels of local government. Progressive change processes, such as metropolisation, Europeanisation, or depopulation of peripheral areas, impact both the legal framework within territorial units (local governments) operate, as well as the practice of their operation and the performance of public responsibilities. In Poland, local government units can traditionally cooperate in three basic legal forms (bottom-up and voluntary): municipal unions, agreements, and associations. However, creating functional connections across administrative borders in metropolitan areas requires the exploration of new legal solutions, such as establishing a metropolitan union. Additionally, Poland’s internal processes are significantly influenced by its membership in the European Union, particularly since the EU adopted the principle of ‘territorial cohesion’. It is undoubtedly one of the key factors that stimulate the development of coordination and cooperation processes at the local level in Poland.