Rotating equipment plays a vital role across a wide range of industries, including oil and gas, refining, manufacturing, and chemical processing. Commonly referred to as turbomachinery, these systems encompass steam turbines, gas turbines, electric motors, and compressors. Many of these machines are essential to core operations and often run continuously for extended periods—sometimes years—before scheduled maintenance or downtime occurs. Any interruption in their operation can have a substantial impact on bothEfficiency productivity and financial performance. As industries demand greater power output, improved efficiency, reduced costs, and more compact designs, turbomachinery engineering has had to evolve rapidly. This evolution has driven the development of advanced analytical tools and more sophisticated design methodologies. Consequently, ensuring high reliability in these machines is not just desirable—it’s imperative. This chapter aims to present a broad overview of rotordynamics, focusing on the physical principles behind the subject while avoiding deep theoretical detail.