Geomagnetism is one of the methods used to probe the Earth's interior Pogo and Magsat satellite missions have permitted the characterization of long wavelength static magnetic anomalies and their interpretation in terms of magnetization distribution in the lithosphere. However very little has been done with satellite magnetic data for studying the distribution of electrical conductivity in the Earth's mantle. My main objective is to use the Magsat and land observatory magnetic data for investigating the electromagnetic induction process within the Earth. I will interpret response functions of the Earth at different periods of the magnetic field with an existing three-dimensional model. The data will then be inverted at regional and global scales to obtain a three-dimensional image of the electrical conductivity in the mantle and hence provide new constraints on its structure and thermodynamical state. The work will benefit from the forthcoming satellite mission Oersted scheduled for 1997.