The Earth’s climate fluctuates and changes both regionally and globally. Inevitably, this is reflected in the variability and change of Earth's water budget and its complex and dynamic energy balance with the Sun. Processes controlling the transports, transformations and exchanges of heat and water in the climate system are inextricably intertwined over a large range of spaceand time-scales from boundary-layer turbulence to global climate change. Recognizing the pressing requirement to better understand and predict these complex processes and their interactions, the World Climate Research Programme (WCRP) launched the Global Energy and Water Cycle Experiment (GEWEX) in 1990. GEWEX leads WCRP’s studies of the dynamics and thermodynamics of the atmosphere, the atmosphere’s interactions with the Earth’s surface (especially over land), and the global water cycle. By virtue of this central role, GEWEX connects with other WCRP projects, including the Climate Variability and Predictability (CLIVAR) project, the Stratospheric Processes and their Role in Climate (SPARC) project, and the Climate and Cryosphere (CliC) project. Furthermore, WCRP’s co-sponsors, WMO), the International Council for Science (ICSU) and the Intergovernmental Oceanographic Commission (IOC) of UNESCO, provide GEWEX access to researchers in both the academic and governmental sectors.