A modal model is a concise and convenient way to describe the dynamic characteristics of a structural subsystem of a vehicle, such as a frame or a body structure. Techniques have been developed for obtaining a modal model by fitting the model to measured frequency responses. These modal models are then used as “building blocks” and coupled to mathematical models of the vehicle's other subsystems (the suspensions, the engine mounting system, etc.) to simulate the total vehicle system.This paper explains the basic theory of modal modeling, including the concepts of mode shape scaling and residual compliances. Some sample vehicle shake simulation studies are also discussed.