Vibration analysis has found widespread application for condition monitoring in a variety of applications and industries. With the continual development of cheaper and more powerful processing hardware, such systems have developed from utilizing simple checks on amplitude to those based around sophisticated spectral analysis. This book presents application of the model based diagnostic method for early detection of faults in rotating machinery. The proposed diagnostics system based on two methods – modal analysis (OMA and OMAX methods) and non-linear signals models (NARX). In the book the diagnostic system based on such modeling is presented. The proposed system was verified during research on a specialized test rig, which can generate vibration signals and on data recorded at wind turbine. In the book, practical aspects of the developed diagnostics system application are also discussed, i.e. sensitivity of the method, complexity of the algorithm and effort needed to apply the method on a real machine.