Here, we introduce the first openly available comprehensive database of magnetotelluric (MT) and related electromagnetic data that we developed and matured over the past decade, explain how to access the data, and describe the challenges that had to be overcome to make MT data sharing possible. The database is a helpful tool for MT scientists, and is widely used by the international scientific community in teaching, planning future surveys, and then to leverage the value of new data at the inversion and interpretation stage. It has also turned into a primary resource for researchers in space weather, and for power grid industry. MT impedance, a transfer function that relates geoelectric fields to geomagnetic fields at the Earth’s surface, provides a critical missing component for estimation of geomagnetically induced currents: quasi-direct currents caused by geomagnetic storms that can destroy valuable equipment and cause extended blackouts. We envision that this database will also be useful for researchers in other areas of geophysics, such as seismology, who would like to use real MT data for hands-on learning and joint inversion analysis.