Commercially used fiber optic measurement methods have different performances because of different physical princi-ples and different sensor designs. Environmental influences, type of application and operational conditions can cause perturbations in the sensor system, depending on the chosen measurement principle. Such perturbations lead to faulty measurements, and thus, the structural behavior can be misinterpreted. In order to ensure reliable measurements, not only the characteristics of the sensor system must be known, but also its ability for the specific use must be proven. This paper points out essential criteria for optimum choice of fiber optic sensor systems and demonstrates necessary steps to evaluate the long-term stability and reliability of a sensor system. The paper summarizes the conditions required for evaluation of a sensor system, and briefly touches on the correct use of vocabulary of general terms in fiber sensor measurement technique to describe the real performance unambiguously. On the way towards drafting guidelines and standards for an appropriate use of fiber sensors, firstly survey of important issues is presented. Two details of these are explained with the example of FBG strain sensors. Finally, when fiber sensors are to be installed on-site, the procedure of validation is presented to assure that the particular requirements for a specific intended use of fiber sensors are fulfilled.