Recent interest in applications of adaptive engine mounts to improve ride quality and passenger comfort has introduced new research areas in the field of vehicle dynamics and control. Introduction of vehicles with smaller engines and lighter and more flexible frames, for the purpose of improving fuel economy, has led to increased frame vibration levels. Frame vibration at engine idle speeds is caused by engine firing and imbalance forces which are transmitted primarily through the engine mounts. Consequently, effort has been focused on improving engine mount technology to achieve better vibration isolation.Introduction of adaptive engine mounts into the dynamics of a flexible engine-frame system requires an integrated study from both vibration and control points of view. This paper presents the results of an on-going research on applications of adaptive hydraulic mounts, manufactured by Cooper Industrial Products, on a Ford Ranger Light Truck. Several issues have been studied which form the fundamentals for optimal implementation of adaptive engine mounts. These include: system modeling, controller design, required sensors, and design of new actuators. The focus of this paper is on the controller design for hydraulic engine mounts. In particular, the issue of open-loop control versus closed-loop control will be discussed and performance of these control schemes once implemented on the actual vehicle will be compared.