Following the motivation of this work, this chapter introduces the basic concepts of continuum mechanics and electromagnetism. Attention is then focused on linear piezoelectricity, elaborating two ways of writing the governing equations: the displacement approach and the stress approach. This leads to variational principles. The final section provides a basis for generalising piezoelectricity—and, by mathematical analogy, piezomagnetism—to random media whose description necessitates tensor-valued random fields.