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Fixed valve lift characteristics and timings of internal combustion engines usually represent a compromise with regard to the requirements placed on power output and torque. In order to minimize the compromise, numerous Variable Valve Actuation (VVA) systems have been proposed that give adjustable valve operation depending on the engine speed. This paper presents a review of VVA systems which have been investigated mainly for the optimization of engine torque. Of most interest are systems which have already been tested in complete engines or even installed in production line cars.