Publisher Summary This chapter discusses the magnetism in artificial metallic superlattices of rare earth metals. Magnetostriction refers to any dimensional changes of a magnetic material caused by changes in its magnetic state. Magnetostriction can originate from changes in magnitude or direction of the applied field or from changes in temperature. Artificial metallic superlattices of the heavy lanthanide elements with yttrium exhibits incommensurate (except Gd) periodic magnetic order that is coherent over several bilayer periods. The features of the ordering, including the phase and chirality coherence observed in [Dy[Y] systems, suggest that the order is propagated by a spin density wave in the Y conduction bands stabilized by the 4f spins. Superlattices with the S-state ion Gd behave similarly, except that the interlayer coupling is only collinear ferromagnetic or antiferromagnetic. The existence of the long-range propagating order is found to be independent of the direction of the net moment component as long as the stacking direction of the superlattice is parallel to the propagation vector of the magnetic structure. In the [Dy[Y] superlattices, the magnetic coherence length is found to be proportional to the reciprocal thickness of the intervening Y layer.