The central, though under-recognized, reason why sustainability is of crucial importance to humanity is because ongoing trends in environmental conditions, at regional and global levels, now jeopardize nature’s life-support systems. This has great implications for human well-being and health—and for the rest of the biosphere (McMichael, 2001). That connection is poorly understood by a generation of policymakers (and researchers!) who have internalized a quasi-Newtonian view of how the world works, and have accepted the neoclassical economic orthodoxy that, via human ingenuity, continuing growth is possible. Currently, therefore, ‘‘sustainability’’ is viewed predominantly in terms of maintaining the assumed upward linear trajectories and moving the global economic engine into ever higher gear. That contrasts sharply with the excellent definition on the Internet’s Wikipedia, referring to sustainability as a system of ‘‘parallel care and respect for the ecosystem and the people within.’’ The ‘‘EcoHealth’’ mix of research disciplines therefore has a dual task: (i) doing research that elucidates these relationships, and (ii) communicating the profound nature of that relationship. Popular culture weighs against ready recognition of this fundamental dependency of health on the natural world. Most people, in day-to-day musings about ‘‘health,’’ assume that the main determinants are personal behaviors, consumer choices, local environmental exposures, access to medical care, and chance. When the natural environment is (apparently) a stable ‘‘constant,’’ then that popular assumption about micro-scale determinants may seem tenable. Today, however, it most certainly is not tenable. Population health depends, more fundamentally, on social and economic conditions, water and food supplies, the integrity of ecosystems, biodiversity stocks, microbial ecology, and climate. Those macro-scale determinants of health are now being destabilized, globally, by unprecedented human pressures. Environmental health research has, for long (and, of course, with many important consequences), studied the effects of localized exposures to specific direct-acting agents (such as heavy metals, pesticides, ionizing radiation, or water-borne microbes). Today, we also face a very different category of environmental health hazard, impinging on human health mostly via systems-based changes to the environment (including climate, food-producing systems, freshwater circulation, and other ecosystem ‘‘goods and services’’). The recent appearance of these larger-scale, and forward-projecting, systemic risks to population health are a fundamental signal that humankind, at global level, is now on a nonsustainable path. This is a remarkable, new situation—one that our generation must understand, analyze, and respond to. This argument has been foreshadowed by Wilcox and Colwell (2005), with particular reference to infectious diseases: