An optical fiber is a dielectric cylindrical waveguide that operates in optical band. The transmission characteristics of optical fibers are determined by their structure and materials. According to the transmission polarization state, SMF can be further classified into non-polarization-maintaining optical fiber (referred to as non-PMF) and polarization-maintaining optical fiber (referred to as PMF). Based on wave theory, this chapter will discuss the transmission and characteristics of polarized light in SMF.