Probiotic Cities covers a body of work that is at the forefront of emerging knowledge within architecture, towards designing informed indoor and built environment microbiomes. Sited within the broader field of Bio Design, the book presents highly experimental design research at the intersection of architecture, engineering and microbiology. The book describes work which explores novel strategies towards directly (re)introducing beneficial microbes into buildings and cities. Through discussion of both the work and the processes and methodologies used, it provides a framework to enable designers and practitioners to begin to engage with contemporary human–microbe relationships towards the design of healthy and resilient cities. The book defines a new microbial paradigm for architecture that engages with broader emerging ecological or ‘more than human’ philosophies for design within the age of the Anthropocene.