This Special Collection deals with the European Union’s Outermost Regions (ORs) and European Overseas Countries and Territories (OCTs), which face specific developmental obstacles as well as serious environmental issues with relevant socio-economic impacts, such as climate change, environmental degradation, land-use change, coastal erosion and loss of biodiversity. Articles to appear in this One Ecosystem Special Issue aim at fostering robust, novel, and cost-effective MAES-related approaches, strategies and applications in the EU's ORs and OCTs.