Geodesy is a suite of powerful Earth-observation techniques, associated methodologies, and analysis tools that today are making a vital contribution to science and society. Yet geodesy is not a new, child-of-technology sciaence. It dates back hundreds of years — some would claim thousands of years, and that the ancient Greeks and other pre-Christian cultures shaped its direction. This is illustrated by its classical definition as the science of measuring and mapping the geometry, orientation in space, and gravity field of the Earth; these days we also include their variations over time. At a practical level, geodetic practice forms the foundation for surveying, navigation, and mapping, and the digital datasets underpinning these activities.