As discussed in Section 9.8 of Chapter 9, dynamic instability leading to self-excited rotor vibration can originate from several different sources. Modern turbomachinery is probably where self-excited rotor vibration is most often encountered, because of the high-power transfers and the attendant fluid dynamical interaction phenomena that abound inside turbomachinery. In most cases, self-excited rotor vibration can lead to excessively high vibration levels, and therefore when it is encountered the mandatory objective is its elimination from the operating zones of the machine. Paraphrasing Professor Stephen Crandall (1983), the available rotational kinetic energy in a machine is typically several orders of magnitude greater than the energy storage capacity of a destabilized rotorwhirling mode, and thus only a miniscule portion of the rotor kinetic energy channeled into an unstable mode can readily cause a failure. Even with the best of design practices and most effective methods of avoidance, many rotor causes of dynamic instability are so subtle and pervasive that incidents of self-excited rotor vibration in need of solutions continue to occur. Three interesting case studies from the author’s troubleshooting experiences are presented in this chapter, all involving large steam turbo-generators. Each of these three cases is unique and thus individually informative.