We are beginning to better understand the complex differentiations of public spaces, and in particular, the ways that more private territories form within public spaces, both formally (e.g. legally permitted sidewalk cafe seating) and informally (e.g. a family picnic on a blanket in a public park). These structures are remarkably complex, intricate and dynamic, and they form as the result of a complex interaction of rules, laws, customs, tacit agreements, and structural adaptations over time. Designers can make use of this knowledge to better support the development of a more dynamic “ecology” of more private zones within public spaces, allowing a more balanced mediation between individual, group and public needs, with fewer conflicts. At the same time, designers and stakeholders can better resist the damage that can occur to the public realm from an over-dominance of private interests. This chapter describes some of the work that has uncovered this structure, and the wider lessons for design and policy.