Symbiotic Collectives examines the social and cultural implications of the symbiosis paradigm that has recently resurged in the life sciences due to the booming research on the microbiome. It asks how the manipulation of symbioses catalyses the emergence of bio-social relations. It focuses on two cases in which the biotechnological intervention in symbiotic relations between host animals and microbes addresses global problems: The modification of bovine ruminal bacteria seeks to reduce the methane production of global cattle populations. The creation of a symbiotic relationship between a bacterial species and a mosquito stops the latter from acting as a vector for infectious disease like dengue fever. The explorative case studies provide a particularly illuminating lens to study the emergence of a distinct mode of biopolitical intervention – symbiotic engineering – that creates novel relations between the living and the social on various spatial scales. By mapping these emerging symbiotic collectives, the project seeks to update concepts of sociality still prevailing in the humanities. The project mobilizes the concept of symbiosis to deepen our understanding of the hybridization of nature and culture. It therefore revisits the sociological use of the symbiosis concept by theorists like Robert E. Park and Niklas Luhmann and tries to arrive at a sociological understanding of symbiosis that takes into account the insights from millennial microbiology as well as the proliferation of symbiotic relations due to symbiotic engineering. The project thus combines explorative case studies with a theoretical concern: the analysis of symbiotic engineering with a theory of symbiotic collectives.