This chapter explores theoretical grounds for the planning of pandemic-proof cities. It begins by revisiting and digesting a body of system-oriented theories from social-ecological systems thinking to Health Ecology, that address the multidimensionality of urban health and resilience in the ecological context of cities. Cities are at the forefront of public health challenges, as they are dense nodes of social, as well as human-animal interaction, providing ideal conditions for infectious diseases to spread. Unravelling the mediating role of built environments for health incorporates both measures of disease prevention and targeted interventions to reinforce affordances for health-promoting behaviour. Exploring the pathways through which urban planning could contribute to a larger systemic transformation towards planetary health necessitates cross-disciplinary efforts and a synoptic systems lens. Theoretical conceptualization is outlined based on the hypothesis that urban systems with high diversity are better able to reprogram, reconfigure, re-imagine, and re-think themselves after adversities.