Abstract: A system for measuring the moisture content of a multi-layer bale of material, comprising a source of microwave radiation disposed on a first side of the bale for directing a circularly polarized source beam through the bale in a direction substantially parallel to the layers thereof so as to exit from the bale as an exit beam and a conveyor for conveying the bale past the source of microwave radiation. A pair of microwave antennas are disposed on an opposite side of the bale for receiving mutually orthogonal components of the exit beam permitting determination of a maximum amplitude of the exit beam corresponding to an amplitude of the exit beam in a direction normal to the layers of the bale. This permits calculation of an attenuation of the beam consequent to absorption by moisture in the bale and thus allows the moisture content of the bale to be determined.