In this paper we consider the propagation of plane electromagnetic waves in a non-absorbing material which is subjected to finite deformations. It is assumed that the material is isotropic when undeformed and when no electromagnetic fields are present and that it is centrosymmetric. The theory is formulated from both Eulerian and Lagrangian points-of-view. The latter formulation rests on the Lagrangian formulation of Maxwell’s equations for a deformed material due to Walker, Pipkin and Rivlin [1].