An earthquake directly affects a structure by increasing the energy within the structural system. A significant portion of this energy can be dissipated and/or reflected through the introduction of a passive, active, or semi-active control system. If certain performance criteria are established which require continuous reconfiguration of the structural system, either an active or semi-active control system will generally be required. In the case of semi-active control systems, the control forces are developed by the motion of the structure itself through appropriate adjustment of the stiffness and/or damping characteristics of semi-active control devices. Further, the operation of semiactive control devices requires a minimal amount of external power. Examples of these devices include electro-rheological fluid devices, semi-active friction devices, and semiactive fluidic control devices. This paper describes semi-active fluidic control devices, the successful use of such, devices in military applications, and the research efforts of the writers in transferring and adapting this technology to the field of earthquake hazard mitigation. The experimental testing of a semi-active continuously adjustable damping device which operates on the principle of fluid orificing is described. Furthermore, mathematical models which describe the behavior of the device are presented.