Three major structures are involved in laboratory simulations of field vibration environments: the test item, the vehicle, and the vibration exciter. The test item is the structure under study and is attached to the vehicle in the field environment. The word vehicle is used here to refer to any structure used in the field to transport, or simply to support the test item. In laboratory simulations, the test item is attached to one or more vibration exciters. The ultimate goal of a laboratory simulation is to define appropriate test item inputs such that its field dynamic behavior can be reasonably simulated, particularly stress levels, natural frequencies, and mode shapes. This paper describes a general theoretical model for laboratory simulations of field dynamic environments. Frequency domain input-output relationships are used to model the structures involved in the simulation process. Matrix partitioned frequency domain equations of motion are written for each structure. Manipulation of these equations with suitable boundary conditions leads to general expressions for the test item interface forces and motions in both field and laboratory environments. These expressions are used to describe four laboratory test scenarios.