This essay charts a conceptual history of “planetary health,” which holds that population health and the continuity of human civilization depend on the integrity—the health—of the Earth’s life-support systems. It seeks to identify settler colonial and imperial genealogies of this distinctly ecological approach to human population health and flourishing, an assemblage of systems theory and planetary thinking as well as developments in environmental sciences and theories of sustainable development. Planetary health may be seen as a “third wave” of disease ecology, (...) an emergent resource for more complex, naturalistic, and scaled-up modeling in epidemiology—the latest installment in the search for multifactorial, relational, and integrated explanations of patterns of disease. The approach required a new planetary imaginary—emerging from a series of Earth-encompassing crises, such as global heating—which enlarged and systematized ecological configurations of human health and illness. In tracing and critically situating this conceptual history, the authors offer a partial perspective on what may yet become planetary health, drawing attention to some other conceptual routes that may be taken. (shrink)