The Earth system changes continuously. Variations in Earth’s interior, the atmosphere, the oceans, and near-Earth space give rise to changes in global fields, particularly in Earth’s magnetic and gravity fields. The underlying processes can be identified and studied through the monitoring and analysis of fundamental geomagnetic and gravity parameters. These are especially suitable to quantifying terrestrial transport mechanisms and solar--terrestrial interactions. This special issue solicits papers that build on data from satellites on low Earth orbits, such as CHAMP, GRACE, GOCE, and Swarm, the latter being of particular interest due to its multi-satellite constellation. In order to improve the understanding of interconnections and coupling processes, submissions are also welcome that bring in further sources of information, such as data from other satellite missions, ground-based observations, and empirical and physical models.