[en] As part of an assessment of the role of dynamic testing in the design of nuclear power plant (NPP) structures, the state of knowledge concerning system-identification methodologies and applications is evaluated. The name system identification is applied to methods determining a mathematical model, and/or its parameters, for a physical system from the input excitation and the corresponding system response. In general, it is found that system identification is limited to parameter estimation for a priori chosen models. The well-developed parameter-identification techniques assume linear behavior of the system. For structural applications the most commonly used method is the modal-analysis technique. Combined software and hardware packages are available commercially to carry out the testing and modal analysis for small structures and components. Nonlinear parameter estimation and generalized system identification are still in the developmental stage