This is the first book to provide comprehensive coverage of the basic theory of propagation in planar waveguides and devices. It offers an accessible and thorough self-contained guide to the understanding and solution of theoretical and practical design problems, concentrating on single-mode buried channel devices fabricated in silica-based technologies. Essential analytical and numerical techniques for determining practical waveguide attributes such as mode propagation, cutoff-wavelength, substrate leakage, bend loss, scattering due to surface roughness and fibre splicing optimization are given. The emphasis is on simple descriptions associated with straightforward analytical and numerical quantification, together with tables of parameter values for practical waveguides. Several basic passive devices are covered in detail, including X- and Y-junctions and evanescent single-mode couplers, as well as optimal curved paths for connecting arrays of these devices. Together these design recipes provide a prescription for total device design, including input, output and connecting waveguides. These planar waveguides and devices are key components of both the photonic chip and the hybrid photonic/electronic chip, which will emerge as hardware for incorporation into future optical communications systems within the information superhighway.