We inhabit a world of severe human-induced ecological overshoot. The ongoing ecological crisis, however, has not been caused equally by all humans. The economic growth-driven world economy is one with great disparities and socio-economic inequality, where the affluence and technologization of the wealthy part of humanity is secured by the labor of others and access to resources. Due to the prevailing socio-economic inequality and differences in environmental impacts between individuals, organizations, and nations, we argue that the primary attention in mitigating the overshoot should be given to the factors of affluence and technology, and only after this we should address the difficult questions related to human population. In the search for a meaningful ethos to study and guide our inquiry in the world of growth and overshoot, we propose applying the concept of sufficiency: the idea of 'enoughness'. Accordingly, in this book, we ask what sufficiency could mean for affluence, technology, and population. Contributors are: Karl Bonnedahl, Michel Bourban, Philip Cafaro, Pasi Heikkurinen, Mikko Jalas, Jessica Jungell-Michelsson, Lassi Linnanen, J. Mohorcich, Iana Nesterova, Tina Nyfors, Thomas Princen, Toni Ruuska, Joonas Uotinen, and Tere Vaden.