Over the last forty years, the circle of organisms thought worthy of inclusion within an ethical framework has expanded markedly, in large part in response to Aldo Leopold’s ‘land ethic’. However, there are still clear limits to the forms of life we are willing to include in such a framework. In this paper I suggest that a strong case can be made for microorganisms to be accorded special ethical status, as they represent the base of all food chains and of the major biogeochemical cycles. Without lions there is life, but without microorganisms there can be no higher life forms. The notion of protecting individual microorganisms may be absurd, but microbial communities and ecosystems nevertheless deserve protection, and offer an example of the merit of a population based approach to environmental ethics. I argue that humankind should assume the position of a moral agent to the microbial world, by formally recognising the intrinsic worth of microorganisms, as well as their utilitarian value to humans and to the rest of life on earth. The practical implications of such an ethic are discussed.