Modern mechanical and aerospace systems are often very complex and con- sist of many components interconnected by joints and force elements such as springs, dampers, and actuators. These systems are referred to, in modern lit- erature, as multibody systems. Examples of multibody systems are machines, mechanisms, robotics, vehicles, space structures, and biomechanical systems. The dynamics of such systems are often governed by complex relationships resulting from the relative motion and joint forces between the components of the system. Figure 1 shows a hydraulic excavator, which can be considered as an example of a multibody system that consists of many components. In the design of such a tracked vehicle, the engineer must deal with many interrelated questions with regard to the motion and forces of different components of the vehicle. Examples of these interrelated questions are the following: What is the relationship between the forward velocity of the vehicle and the motion of the track chains? What is the effect of the contact forces between the links of the track chains and the vehicle components on the motion of the system? What is the effect of the friction forces between the track chains and the ground on the motion and performance of the vehicle? What is the effect of the soil–track interaction on the vehicle dynamics, and how can the soil properties be charac- terized? How does the geometry of the track chains influence the forces and the maximum vehicle speed? These questions and many other important questions must be addressed before the design of the vehicle is completed. To provide a proper answer to many of these interrelated questions, the development of a detailed dynamic model of such a complex system becomes necessary.