A resetting semi-passive stiffness damper (RSPSD) for use in damping movement. Embodiments of such a RSPSD include, for example, a pistoned cylinder connected to a grooved rack, and a spring-loaded lever arranged between the rack and a slotted channel above the rack. One end of the lever is allowed to move pivotably and vertically within the channel as the other end moves with the rack. A sensor is provided and communicates with a bypass valve on the cylinder. A change in the direction of movement of the rack forces the lever further into the slotted channel where it eventually triggers the sensor, which then sends a signal to open the bypass valve. As the rack continues to move, the lever eventually reverses direction, and is forced back down the slotted channel by a return spring. Upon leaving the sensing range of the sensor, the valve is signaled to close.