Using recent developments in social theory, this book offers questions about how bacteria, viruses, microscopic materials and societies develop in tandem. The examples discussed – from urban infrastructures to the medieval plague and from antibiotic resistance to epigenetics –develop an account of how previous and present arrangements make some futures more likely than others and how unequal patterns of exposure and entanglement arise. This book aims to demonstrate the relevance of social and practice theories by overcoming classic distinctions between the very small and the very large, between agency and structure, and between nature and culture.