Eco-sufficiency, or simply sufficiency, refers to the concept or strategy to reduce the environmental footprint of societies through moderating the need for energy, carbon and material-based services and products. The term was popularised by authors such as Thomas Princen, a professor at MIT, in his 2005 book ‘The Logic of Sufficiency’. As a goal, sufficiency is about ensuring that all humans can live a good life without overshooting the ecological limits of the Earth, while at the same time defining what that good life may consist of. Princen argues that ‘seeking enough when more is possible is both intuitive and rational - personally, organizationally and ecologically. And under global ecological constraint, it is ethical.' In order to operationalise sufficiency, principles and ideas of concrete actions and policies have been proposed by various authors. Sufficiency may be approached at the individual level as a personal attitude or life philosophy (such as in the ‘Sobriété heureuse’ concept of French environmentalist Pierre Rabhi, or Schneidewind‘s concept of the ‘Good Life’), as well as a core collective value that could amend the notion of liberal societies. In terms of lifestyles, it is strongly related to the concepts of voluntary simplicity and downshifting. There are significant barriers to the widespread adoption of sufficiency, as it goes against current dominant social paradigms (economic growth focus, materialism, individualism, etc.). However, there are signs of change in some trends, be they motivated by environmental concerns or other co-benefits. Sufficiency usually triggers debates around the notions of needs, wants, and 'enoughness'. Its impact on the economy and the role of rebound effects are also challenges to be addressed. The war in Ukraine and subsequent energy crisis in 2022 have put a significant pressure on energy supply, notably in Europe, and popularised the concept of sufficiency and sufficiency policies. For instance, France has published a national energy sufficiency plan in October 2022 ('Plan national de sobriété énergétique'). Background Definitions Sufficiency (also called ‘eco-sufficiency’) is a concept that relates both to an ideal and a strategy to achieve it. As a goal, sufficiency is about ensuring that all humans can live a good life without overshooting the ecological limits of the Earth (for now and generations to come), and defining what that good life may be made of. As an increasing number of experts consider that technical progress and greener technologies alone will not be enough to achieve this goal, sufficiency