This paper and a companion paper present a state-of-the-art review of significant research performed in the area of smart structures. The focus of the review is journal articles published since 1997. This paper reviews articles on active and-semi active control of structures using a variety of systems. Active control systems include active tuned mass dampers, distributed actuators, active tendon systems and active coupled building systems. Semi-active control systems include: magnetorheological (MR) fluid dampers, semi-active stiffness dampers, semi-active tuned liquid column dampers, and piezoelectric dampers. A review of hybrid control systems and control strategies is presented in the companion paper.