The term 'sufficiency' refers to a strategy of introducing hard limitations to unsustainable trends—in particular to overconsumption—plus an emphasis on distributional justice in order for everyone to have access to enough resources to meet their needs.

Sufficiency policy complements the eco-efficiency approach that so far has been the main focus of the sustainable development debate. In order to keep the world economy within planetary boundaries, more must be done than just focusing on eco-efficiency as proponents of 'green growth' have claimed so far. Due to the 'rebound effect', an increase in eco-efficiency does not inevitably lead to a decrease in the use of natural resources and energy in absolute terms.

However, a sufficiency approach is not meant to disparage the value of eco-efficiency, but rather it tries to harness its true potential: once sufficiency is accepted as a necessary pre-requisite for sustainability, eco-efficiency is then correctly seen as a tool for affluence maximization. In other words, while sufficiency includes setting an 'ecological ceiling' for the amount of natural resources used by the economy, eco-efficiency aims at generating a maximum of goods and services from that capped amount of resources. This is an essential understanding to move beyond the 'gospel of eco-efficiency'.

While embracing environmentally friendly behaviours is a step in the right direction, it must be acknowledged that we are locked in an unsustainable system that encourages overconsumption and limits our ability to pursue low-impact lifestyles. Thus, sufficiency is not predominantly an appeal to consumers, but rather a political challenge, a call for transformative change. As our individual behaviour within the system can bring about only marginal changes, we have to collectively engage in changing our economic model if we want to revert the current ecological overshoot and build a sustainable economy.

As for poor people in the Global South, it is undeniable that they have a 'right to development'. However, the majority of the world's poor are now living in middle income countries. As a result, the growth imperative does not apply to countries any longer, but to disadvantaged groups, with redistribution of wealth between the rich and the poor in each country, between countries and between the global consumer class and the rest of humanity a key issue. Hence, the priority should be to enhance material well-being of the poor worldwide while simultaneously reducing global aggregate material throughput. The basic principle of intragenerational equity entails that wealthy households in all countries should consume less to free up the 'environmental space' needed for justifiable consumption increases among the poor.

New policy instruments should be designed to bring about ecological fair sharing and a new economy based on the concept of 'sufficiency'. These instruments should facilitate an equitable downscaling of industrialised countries' environmental throughput, namely the rate at which they process and transform energy and raw materials. And since a constant increase in the transformation of natural resources into goods and services is ingrained in our current economic system, this downscaling will challenge the current economic structures, mechanisms and their legitimation, in particular the fundamental belief in the feasibility of infinite economic growth.

This implies a new direction for societies, one in which they will organise and live differently from today. The sufficiency transformation would entail that people work fewer hours in paid employment, share jobs and services in many cases, and lead more convivial and less materialistic lifestyles overall. Although economic activity would be more localised, the state would have an important role both to limit material and energy use, and redistribute income and wealth. This last one is an essential element of a sustainable and equitable economic system: if we limit GDP growth then the only way to increase the monetary income for the less well-off in society is through a process of redistribution by reducing the income share of the richest and shifting it to the poorest.

Between the unsustainable extremes of overconsumption and material poverty lays fair sharing and sufficiency, which is about using 'enough' for humans to flourish without compromising the stability of the biosphere.