This chapter contains sections titled: Modes in optical waveguides Discrete waveguide modes Field distribution of the modes Waveguide couplers and beam splitters External coupling Coupling between waveguides 3 dB couplers for beam splitting Branching waveguides Waveguide optical modulators The electro-optic effect The electro-optic phase modulator Polarisation modulator — dynamic phase retarder Integrated intensity modulators Electro-optic directional couplers Applications of waveguide optics Waveguide optics in optical interconnects Waveguide optical sensors List of new symbols Exercises References