This fourth edition of an enduring and popular book has been fully updated and revised, exploring the two opposing paradigms of sustainability in an insightful and accessible way. Eric Neumayer contends that central to the debate on sustainable development is the question of whether natural capital can be substituted by other forms of capital. Proponents of weak sustainability maintain that such substitutability is possible, whilst followers of strong sustainability regard natural capital as non-substitutable. The author examines the availability of natural resources for the production of cons.