In the project RMT-monitoring funded by the European Union, a new radiomagnetotelluric device has been developed which can record time series of electric and magnetic fields in a wide frequency range from 10 kHz to 1 MHz. Transfer functions are determined by spectral analysis using a newly developed processing software. A workbench program has been developed in which the transfer functions are interpreted with conductivity models based on new inversion algorithms. The developed tensor radiomagnetotelluric device was tested in the laboratory and then applied successfully in the field to several environmental and groundwater problems in Russia, Ukraine, Denmark, Romania, and Germany. The observed transfer functions in the field are the first ones worldwide in the frequency above 250 kHz which leads to a better resolution of the shallow structure. The new device enables quick and efficient mapping of polluted areas and supports tensor measurements allowing a 2D or 3D interpretation of the field data.