The determination of a building's modal parameters (natural periods and mode shapes) using ultra-low level forced vibration testing and analytical modeling were critically compared. The structure utilized for this experiment was the Robert E. Kennedy Library on the campus of California Polytechnic State University San Luis Obispo, a five-story reinforced concrete shear wall structure. The specific testing procedure used has been verified to produce accurate results in smaller buildings, but the Kennedy Library represents the most massive subject structure.