Environmental movements have always dealt with intrinsically transnational issues. At the same time, many issues and strategies among environmental movement actors have been articulated as nation-based. An increased emphasis on the issue of climate change and preparations before the UN Climate Summit in 2009, held in Copenhagen, fuelled the mobilisation of both new and established environmental movement actors in Denmark. The 2009 Climate Summit in Copenhagen has been described as a failure, with claims that it led to a lost belief in international negotiations and a strategy among environmental movement actors to “go back to the national”. This article explores various forms of transnationalisation in connection to the environmental movement and the issue of climate change. We analyse the transnationalisation of the environmental movement within a particular domestic context—Denmark. Our study draws on semi-structured interviews with representatives of, and documentation from, eight environmental movement organisations in Denmark, as well as observation field notes and informal interviews with Danish movement participants and other key actors during the UN Climate Summit 2013, in Warsaw, Poland; 2014, in Lima, Peru; and 2015, in Paris, France. We conclude that climate change as an overall national and transnational agenda for established Danish environmental movement organisations can be understood through various forms of transnational processes that exist simultaneously and that link the domestic and the transnational in multiple ways.