Abstract
The current environmental crisis requires transformative change: Change not only of systems but also of individuals. In this chapter we demonstrate the significance of mental well-being of humans when promoting planetary well-being. We show how mental well-being is linked to nature-connectedness, in promoting pro-environmental behaviour among individuals, and present a view of the human mind (psychological functions) as a part of nature, rather than separate from it. After introducing several theories and concepts relevant to these topics, we provide a closer look at the nature-based intervention Act with Nature. This intervention centres on the idea that nature experience, and especially increasing nature-connectedness through emotional and social support, promotes both well-being and pro-environmental behaviour. We argue that that human's innate ability (and need) to experience the self in connection to physical and social surroundings is vital for promoting pro-environmental behaviour and generating positive impacts on planetary well-being.