This paper explores the way the idea of sustainability is linked to categories traditionally examined by the general systems theory—the categories of system, environment, and complexity. Toward this end, the paper builds upon the social systems theory of Niklas Luhmann to explain the nature of the trade-off between complexity and sustainability. Exemplified by Luhmann's theory of ecological communication, the trade-off emerges because the growing systemic complexity entails the increasing risk that systems develop insensitivity to those environmental conditions on which they critically depend. The key implication of the trade-off is that it may be rational for social systems to withdraw their internal complexity to maintain their sustainability in a given environment. Copyright © 2012 John Wiley & Sons, Ltd.