Leslie Paul Thiele is Distinguished Professor in the Department of Political Science at the University of Florida and served as the founding director of its Sustainability Studies Program. His central concerns are the responsibilities of citizenship and the opportunities for leadership in a world of rapid technological, social, and ecological change. His books include Indra’s Net and the Midas Touch: Living Sustainably in a Connected World (2011) and Sustainability (2013), as well as several others. In this essay, Thiele begins by providing a brief history of the concept of sustainability and its practice. He then turns to Aldo Leopold, the father of modern ecological thinking, and describes the fundamental lessons Leopold taught about the complex web of interdependence between human beings and the natural world, and the dangers of unintended consequences in the wake of human behavior. Taking seriously Leopold’s injunction to “think like a mountain,” Thiele concludes with a set of meditations on what he takes to be the contemporary requirements for living sustainably in an interconnected world where our actions have not only local consequences, but global ones as well.