Fluorescence spectroscopy is an important analytical technique that has been widely used in a variety of applications, such as biomedicine, biology, and science of materials, because it presents some properties which makes it unique, that is, extraordinary sensitivity and selectivity, short delay time (<10(-9) s), and it is neither invasive nor destructive, so it can be used for in situ measurements. Generally, intrinsic fluorescence of many materials, like polymers, is unspecific so it is not useful to analyse their properties or to be correlated to changes in their microenvironment. The incorporation of additives with fluorescent groups would be necessary. When the fluorescence emission of these molecules is sensitive to changes of properties, such as polarity, fluidity, order, molecular mobility, pH, or electric potential, they can be used for detecting such changes in their microenvironment, and they are called fluorescent probes. As long as these probes can follow processes of practical interest, they can be employed as sensors, if the information given by the measure of fluorescence adequately reflects the changes in the system. In addition, a sensor must fulfil some other requirements in order to make them of practical use, the most important being that the material support in which the sensor molecule is inserted. This support should permit a rapid detection of the process and should allow easy processing in a variety of forms. Polymers are well-known systems in which estimation of local parameters are possible by means of fluorimetric techniques. It allows the study of dynamic processes of interest, such as polymerization kinetics and mechanisms, thermal transitions, photodegradation, swelling morphology changes, and so forth.