The paper explores and compares the aims of the three most common legal forms of inter-municipal cooperation in Poland (engaging rural, urban-rural and urban municipalities) during the years 1990-2018: Mono-sectoral Special Purpose Unions, Municipal Associations and cross-sectoral Local Action Groups. Content analysis was applied and development priorities from the statutes and strategies were studied. The main form of territorial association evolved from, initially, mono-functional bodies concerned mainly with local infrastructural investment and managed solely by a group of local authorities, to a devolved type, consisting of multi-purpose associations managed with the participation of economic and third sector representatives. This was the result of the European Union policy of promoting territorial governance and integrated development in functional regions, this being considered as part of the process of Europeanisation. However, these successive forms of municipal cooperation do not appear to have replaced the pre-existing forms, but they have introduced additional modes of governance of local resources. The findings show that the most "integrated" and "sustainable" management of local resources is observed mainly in cross-sectoral partnerships, like Local Action Groups, but not so often in mono-sectoral municipal unions and associations led solely by local government and focused more on hard infrastructure and municipal facilities. However, given the specialisation shown by each of the three types of association, it is likely that the full range of development possibilities in the areas concerned can only be realised if all three forms of cooperation are present. The analysis confirms the positive role of local economic and social sector participation in shaping sustainable development. The findings also indicate the utility of the concept of cross-sectoral territorial partnerships in post-socialist and post-authoritarian countries lacking traditions of grassroots or participative development.Sustainability 2019, 11, 5890 2 of 21 be seen as facilitating a "neo-endogenous" or "integrated place based" model of development, in contrast to a top-down, exogenous and sectoral model focusing on single issues such as transport or agriculture and managed solely by government [4][5][6]. The place-based, neo-endogenous model implies central government support for regional and local bottom-up initiatives for development and well-being, facing one particular territory (natural or economic region, agglomeration, etc.), often requiring cooperation between stakeholders from fragmented administrative areas [7][8][9]. Integrated planning in this context is understood to involve drawing together local social, economic and ecological issues, rather than focusing only on, for instance, technical infrastructure [10]. It is often closely related to "sustainable" development, which involves an additional concern with long-term retention of local natural resources [11][12][13]. In the countries where these processes first emerged,...