This dissertation investigates the active structural acoustic control (ASAC) of sound radiated from a smart cylindrical shell. The cylinder was equipped with piezoelectric sensors and actuators to estimate and control the sound pressure that radiates from the smart shell. Two approaches were studied in this thesis to attenuate the radiated sound. The fist approach is based on using virtual microphone and the second approach utilized the radiation modes of the cylinder. The estimated pressure is referred to as a virtual microphone, and it can be used in control systems instead of actual microphones to attenuate noise due to structural vibrations. To this end, the dynamic model for the smart cylinder was derived using the extended Hamilton’s principle, the Sanders shell theory and the assumed mode method. The simplified Kirchhoff-Helmholtz integral estimates the far-field sound pressure radiating from the baffled cylindrical shell. A modified higher harmonic controller (MHHC) that can cope with a harmonic disturbance was designed and experimentally evaluated. The experimental tests were carried out on a baffled cylindrical aluminum shell in an anechoic chamber. The frequency response for the theoretical virtual microphone and the experimental actual microphone are in good agreement with each other, and the results show the effectiveness of the designed virtual microphone and controller in attenuating the radiated sound. Radiation modes and radiation efficiencies were obtained for the cylindrical shell. The first radiation mode is the efficient mode in radiating sound to the surrounding environment in low frequency domain, therefore, by omitting this mode, most of the radiated sound can be attenuated. This approach was modeled and simulated and its results were compared with those of the conventional active vibration control. As a middle goal an active vibration control of the cylinder was implemented using a multi-input multi-output LQG controller. This controller achieved a good suppression of vibration of the cylindrical shell in a broadband frequency domain. Keywords: Active structural acoustic control, Cylindrical shell, piezoelectric, Virtual microphone, Radiation mode, Radiation efficiency, Modified higher harmonic control, LQG.