This chapter departs from classical theories viewing environmental behaviour as individual choices and focuses instead on how collective action in environmental communities impacts behaviour and societal changes. The chapter discusses four different ways through which Danish environmental communities (eco-villages, food cooperatives, and environmental associations) make a difference. (1) Environmental communities create collective identities and a process of norm convergence among members. (2) Environmental communities design new physical and social infrastructures influencing behaviour, first at the grassroots level and then with spillover effects in local municipalities. (3) Because there is a continuous turnover among community members, the information that people learn and acquire while they are members of an environmental association is spread to the wider community when they leave it. (4) Environmental associations influence policy-makers either because their members tend to be fiery souls and idealists who are more likely to engage into local politics than others or because the size and dynamism of these associations make them interesting to the media and politicians. Environmental communities thus influence society as collective identities, as new infrastructures, as educational institutions, and as political institutions. All these aspects are grounded in collective action rather than in individual choices.