Soil is a functional interface of all terrestrial environments, whether natural, agricultural, or urban. To understand soil, its role, and its functions, it is essential to place it within the broader functioning of ecosystems. The first part will focus on the principles of ecosystem functioning, soil formation, and the properties that determine how humans use them.Urban soils are often degraded, contaminated, and scarce in cities. The second part will explore their crucial role in water and climate regulation, as well as potential strategies for their rehabilitation.Urban Soils: (Part of) the Solution for Sustainable Cities?