Stockholm was the first to win the ‘Green Capital of Europe’ award: in 1976, it adopted its first comprehensive environmental programme and by 2010 it already had projects and dedicated environmental departments with expert groups to plan sustainable urban development and protect its biodiversity. Everything is easier in a city with less than one million inhabitants and a low population density, a capital city that extends over fourteen islands (between lake and sea), where the total green space per person is 70 square metres (mostly woods, forests and nature reserves). The ‘Nationalstadsparken‘, the first national park in the centre of a large city, covers 27 square kilometres, but there are another eleven nature reserves and a cultural park where farms and livestock farms used to be located: as the farmers left, the municipality preserved the environment by leaving horses and sheep to graze and by renovating the buildings. Citizens can now grow fruit, plants and vegetables in more than eighty social gardens rented at subsidised prices. The archipelago of thirty thousand islands, islets and reefs in which the Stockholm metropolitan area is embedded is also an extraordinarily rich ecosystem. However, what defines the uniqueness of the Swedish capital is not the percentage of green, but the way in which it takes care of it: for Stockholm, the protection of biodiversity is part of a general plan that implies reducing CO2 emissions by thinking about the air we breathe, the water we drink and the damage caused by noise on people and animals. Based on these priorities, the city develops integrated long-term plans, which engage the authorities together with citizens. Biodiversity is one of the key ecosystem services to achieve the goal of zero emissions by 2030: working to preserve it has far-reaching implications, with long-term consequences, so it is essential to make citizens aware of the need to change their lifestyles, educating them to use resources more efficiently and sustainably. This does not mean stopping the development of the city: the chapter on the protection of biodiversity in the latest environmental plan approved by the municipality (three-year period 2020-2023) recognises that there is a great need for housing, public and commercial services and expanded infrastructure, but the commitment is to design new neighbourhoods while minimising intervention and impact on the ecosystem. Data is collected on the natural value of the area for which a building project is being submitted: this means knowing which plant and animal species are found in the area and especially whether they are ‘umbrella species’, i.e. animals or plants whose conservation indirectly leads to the conservation of other species in the ecosystem. Urban planning tries to minimise the impact on ecological values as much as possible: for example, the position, shape or height of buildings is changed so that valuable trees do not have to be cut down, or so that their shade does not prevent a natural area from having the light it needs to develop. Stockholm opens itself up to biodiversity above all with ecological corridors, recognised by experts as one of the best ways to mitigate the negative effects of anthropisation on ecosystems: every urban area in every neighbourhood must be connected by green corridors, so the development of the city must strengthen them and not hinder them.