Earth's Critical Zone is the heterogeneous, near surface environment in which complex interactions involving rock, soil, water, air, and living organisms regulate the natural habitat and determine the availability of life-sustaining resources. It is bounded by the top of the vegetation canopy and reaches below the surface to where processes respond to those at the surface over a time-scale of decades to millennia. Physical, chemical and biological processes within the critical zone can be profoundly affected by climate-change, and in turn these processes regulate the composition of Earth’s atmosphere. Systematic observations of the critical zone within dedicated observatories and across the continents are for the first time tackling both the internal dynamics and the two-way feedback that underpin the development of holistic models of climate change impact. In this symposium, leading experts discuss key challenges in critical zone research.