Chapter 14 describes the fundamental understanding of guiding lightwaves in planar and circular optical waveguides. A brief fundamental derivation of the wave equation from the Maxwell's equations is given for symmetric planar waveguides leading to the phenomenon of guiding in optical fibers and circular optical waveguides. Only geometrical parameters of optical fibers are presented here. The attenuation and dispersion effects of modulated lightwave signals can be found the first section (Section 14.2) of this chapter. However, nonlinear effects are given here so that the distortion impacts on signals can be discussed in the next chapter. Chapter 14 gives a brief account of optical fibers (circular 3D optical waveguide) that are commonly employed to establish optical transmission lines.