This chapter argues that polymer fiber Bragg grating (POFBGs) have potential for use in a range of niche applications where the material properties of the constituent polymer provide advantages over silica. The first application of a POFBG — as a widely tunable laser cavity mirror — was demonstrated in 2006, their use was initially limited due to the need to butt couple the POF to a low-loss silica fiber. Polymer fiber sensors offer increased stress sensitivity and a larger strain range. When used to monitor compliant structures, they perturb the mechanical behavior of the structure less than the much stiffer silica fiber. For both silica and POF, even in the elastic region, the relationship between stress and strain is nonlinear, with the nonlinearity for POF being an order of magnitude greater than that of silica. For practical purposes, the nonlinearity may need to be taken into account for strains above about 1% for POF and 3% for silica fiber.