The magnetoelectric effect is a reversible coupling between a piezoelectric phase and a magnetostrictive phase, meaning, a changing magnetic field may be used to generate a potential difference or vice versa. Formally, this is more accurately described as a change in polarisation with a change in the magnetic field. While this effect has been observed in selected materials, it is more commonly seen in composites which combine a piezoelectric material with a magnetostrictive one, with coupling occurring at the interface. Over the past decades, research in this area has come in and out of fashion with the advent of new materials, geometries and fabrication processes, each of which bring magnetoelectric devices closer to the point of usefulness (Fig. 3.1).