Observations have always informed critical decisions and knowledge building throughout human history. Earth observations are a critical ingredient for understanding and predicting the sustainability or disruption of natural services that support basic human needs including water, food, energy, mineral resources, and safe habitation. Such observations are collected by seismic networks, atmospheric and ocean-based sensors (detecting, e.g., ozone, greenhouse gases, ocean currents, sea ice extent), river and tide gauges, and satellites that observe changing terrestrial features including receding glaciers, growth of deserts and urban centers, and evolving vegetative covers. One pressing challenge is to develop terrestrial observatories that could document and inform prediction of the multi-scale and less visible transport of energy and material, and evolution of the Earth's critical zone. This zone -the thin veneer of Earth that extends from the top of the vegetation to the base of weathered bedrock- is critical because it is where fresh water flows, soils are formed from rocks, and terrestrial life flourishes. This zone provides most of the ecosystem services on which societies depend. Its intrinsic resilience, natural evolution, and fate in the face of human land use and climate change needs to be understood and predicted in order to inform our strategies for sustaining a wide range of human activities. Unprecedented pressures are being placed on the critical zone, and understanding the interrelated processes, system dynamics, sensitivities, and thresholds in this zone is of vital importance for informing human decisions. NSF seeks proposals to establish a networked set of Critical Zone Observatories (CZOs) that will address pressing interdisciplinary scientific questions concerning geological, physical, chemical, and biological processes and their couplings that govern critical zone system dynamics. The CZOs are expected, collectively, to 1) measure and quantify the significant processes of the critical zone on appropriate time and space scales; 2) develop a unifying theoretical framework that integrates new understanding of coupled hydrological, geochemical, geomorphological, sedimentological and biological processes; and 3) develop, couple and validate system-level models to predict how the critical zone responds to external forces such as anthropogenic, climatic, and/or tectonic processes. Each observatory must contribute to strengthening the scientific basis for decision-making, particularly with regards to impacts on health, safety, and environment due to observed and predicted changes in the critical zone.An overarching goal of the critical zone observatory network, which will be comprised of US-based sites (50 states plus territories), is to offer scalable and transferable information that could enhance the scale and scope of the knowledge building and societal benefits that will accrue beyond where the specific CZOs are located. Amongst the strategies contemplated in this program are diversifying the coverage of observatories in terms of geography, geology, and types of environments; leveraging existing infrastructure and legacy data; coordinating observations, data management, modeling, and educational activities among CZOs; and coordinating activities that address common questions at multiple observatories. All CZOs will be expected to collect a common set of measurements in addition to site-specific measurements describing the geological, physical, chemical, hydrological, and biological characteristics of the site. In addition, it is anticipated that the CZOs will adhere to common data management policy and use common data management tools. The network of CZOs will additionally serve as a community resource to engage investigators beyond the CZO awardees in critical zone research.