This chapter provides an introduction to surface polariton. Surface polariton is an electromagnetic excitation that propagates along the planar interface between two semi-infinite dielectric media and is localized to the interface in the sense that the amplitude of the excitation decays exponentially with increasing distance into each medium from the interface. The surface polaritons in two-layer systems is described. The simplest structure that supports surface polaritons is the planar interface between two semi-infinite dielectric media. The media can be optically isotropic or anisotropic. The surface polariton at the interface between vacuum and an n-type semiconductor is called a surface plasmon polariton. The dispersion curve for surface polaritons at the interface between a diatomic, cubic, polar crystal, with two ions in a primitive unit cell, and vacuum is shown. The dispersion curve for surface polaritons at the interface between vacuum and a simple, free electron metal is also depicted.