Most of us are familiar with probiotics added to milk or yogurt to improve gastrointestinal health. In this ambitious and original work, Jamie Lorimer offers a sweeping overview of diverse probiotic approaches and an insightful critique of their promise and limitations. Lorimer describes cases in which scientists and managers are working with biological processes to improve human, environmental, and even planetary health, pursuing strategies that stand in contrast to the antibiotic approach: Big Pharma, extreme hygiene, and industrial agriculture. The Probiotic Planet focuses on two forms of rewilding occurring on vastly different scales. In both cases, the goal is to improve environmental health, whether the environment being managed is planetary or human. Lorimer argues that, all too often, such interventions are viewed in isolation, and he calls for a rethinking of artificial barriers between science and policy. He also describes the stark and unequal geographies of the use of probiotic approaches and examines why these patterns exist. Informed by deep engagement with microbiology, immunology, ecology, and conservation biology as well as food, agriculture, and waste management, The Probiotic Planet offers nothing less than a new paradigm for collaboration between the policy realm and the natural sciences.