This chapter presents a broad view of some of the published and most used techniques and schemes for sensing with polymer optical fibers (POF), and presents a small part of the sensing devices using POF since the same techniques can be used to measure several different parameters with slight modifications. In quest for low-cost ways of parameter measurement using POF, different approaches can be found in academia. The most common method of detecting is based on intensity variation which requires simple operation principles and instrumentation. One of the extrinsic sensing techniques employed and commonly used is the light transmission configuration. In the intrinsic sensing techniques, light does not physically leave the fiber but tries to promote the interaction of its evanescent field with the external medium. Intrinsic sensors can be produced not only by changing the structure of the fiber but also by altering the refractive index of the fiber waveguide in the sensing area by ultraviolet or infrared-light exposure.