In order to reduce the vibrational level of lightweight composite structures, active vibration control methods have been applied both numerically and experimentally. Using the classical laminated beam theory and Ritz method, an analytical model of the laminated composite beam with piezoelectric sensors and actuators has been developed. Smart composite beams and plates with surface-bonded piezoelectric sensors and actuators were manufactured and tested. It is found that the developed analytical model predicts the dynamic characteristics of smart composite plates very well. Utilizing a linear quadratic Gaussian (LQG) control algorithm as well as well known classical control methods, a feedback control system was designed and implemented. A personal computer (PC) was used as a controller with an analogue - digital conversion card. For a cantilevered beam the first and second bending modes are successfully controlled, and for cantilevered plates the simultaneous control of the bending and twisting modes gives a significant reduction in the vibration level. LQG has shown advantages in robustness to noise and control efficiency compared with classical control methods. In this study examples of control spillover are demonstrated via the instantaneous power spectrum of the sensor output.