Electroporation is a phenomenon caused by electric field of appropriate strength and duration applied to the cells, which leads to an increase in the permeability of the cell membrane for various molecules that cannot otherwise be transported through the transmembrane. Since membrane electroporation is a consequence of an induced transmembrane potential that is directly proportional to the local electric field, magnetic resonance electrical impedance tomography (MREIT) has been proposed to reconstruct the electric field distribution during electroporation. MREIT allows the determination of the electric field distribution by measuring the electric current density distribution and the electrical conductivity of the treated subject during the application of electric pulses using an MRI scanner and numerical algorithms. MREIT provides an electric field distribution that is a time average of the changing time course, so that all consequences of the change in conductivity of the treated tissue due to electroporation are not neglected in the obtained electric field distribution. The feasibility of this method was demonstrated by determining the electric field distribution during electroporation in silico, in agar phantoms, plant tissues, and animal tissues ex vivo and in vivo. In this chapter, the mathematical framework of MREIT and the concept of electric field distribution monitoring are presented together with the basics of electrical conductivity imaging. In addition, maps of the electric field distribution during electroporation of different tissues are presented, which were obtained by means of MREIT.