In this paper, generalized impedance boundary conditions (GIBC) are derived at an interface between isotropic, homogeneous dielectric media. The advantage of this technique is that rather than requiring that the tangential components of the E↘ and H↘ fields be continuous over the interface, an equivalent set of boundary conditions involving the electric field and its space derivatives is applied, reducing the problem dimension and therefore the computational needs significantly. The equivalence between the two sets of boundary conditions is validated for the case of an infinite dielectric slab. Finally, an application of the concept of GIBC to the analysis of dielectric waveguiding structures for high-frequency applications is described.