This Special Issue Reprint focuses on the study of the preparation phase of earthquakes, searching for possible coupling between the lithosphere, atmosphere, and ionosphere before their occurrences. The topic is afforded by investigating data from the lithosphere (earthquakes' catalogs and seismic tomography), atmospheric parameters-especially from remote sensing satellites-and in situ ionospheric observations from China Seismo Electromagnetic Satellite (CSES-01) and Swarm constellations. Other satellite and ground data are used to corroborate the analyses and better understand the preparation phase of earthquakes across the world. Several methods of investigation are implemented, from statistical approaches to single case study analyses. Modern techniques, such as machine learning, are also applied to predict the standard value of the parameter under analysis and consequently detect possible anomalies eventually induced by earthquakes.