This thesis describes a new actively controlled torsional damper, developed to reduce oscillations caused by the nonuniform torque of internal combustion engines. With the use of an adaptive feedforward control scheme this damper achieves a high effectiveness. At the same time it is very energy-efficient due to a new way of placing the actuator. The effectiveness and efficiency of the new damper are motivated theoretically and they are verified by test rig results obtained with a test carrier.