System identification is a powerful tool in engineering. Its various methods in the frequency and in the time domain have been extensively discussed in earlier CISM courses. The aim of this course is to describe the state of the art in specific application areas, such as estimation of eigenquantities (in the aerospace industry, in civil engineering, in naval engineering etc.), noise source detection, fault detection by investigation of dynamic properties, such as machine sound characteristics, and the identification of the dynamic behaviour of flow induced systems (e.g. aerolastic problems). Geotechnical applications are also among the fields of interest. The lecture notes contain demonstrations of several methods and include a valuation by combining various kinds of experience. Such complex information includes not only theoretical aspects of identification but also advice on practical handling, for example concerning testing effort and data handling.