Active and semi-active suspensions are devices designed to improve the comfort and road-holding performance of the vehicle. Considered as one of the most advanced technologies in the automotive field, they allow to control the suspension motion by acting on its damping characteristics (semi-active and active), to perform energy recovery functions (active) and to provide active forces to the suspension (active). The semiactive device can induce a variable damping without requiring high energy levels and with reduced costs. The active system, instead, needs more supplied energy, higher costs and produces an overall actuation force for controlling the suspension motion. In the last years both solutions have been studied and developed in different forms with peculiar features, with the common purpose of enhancing the performance of a conventional fixed-damping suspension system.