1. Analyzing and predicting vibration behavior of structures is important in the design and development of mechanical systems. 2. A rotor refers to a mechanical system in which at least one part rotates with a very high angular momentum. Vibration analysis of rotor systems requires special knowledge because of several unique behaviors of the structure stemming from rotation effect, which is not observed in non-rotating structures. 3. These concepts specific to rotors are the gyroscopic effect, Coriolis effect, spin softening, rotating damping, and mode directivity. The concepts of the gyroscopic effect, Coriolis effect, and spin softening are critical in the rotor dynamics field. 4. The application of finite element analysis (FEA) to rotordynamics allows for modeling rotors that have complex geometry, which however requires sound understanding of basic concept and theory of rotordynamics and the constraints of existing FEA software.