The aerodynamic causes of suspension bridge oscillations, i.e., vortex theory, flutter theory, and negative slope theory are examined. Thirteen factors to be considered in the design of a suspended span are listed. Frequencies of antisymmetrical and symmetrical modes of vertical oscillation are given and also a minimum frequency in torsional oscillation. Mathematical studies are confined to the suspended span. Seismic studies give a mean fundamental period for the suspended span of 4.5 sec (13.3 cpm) and peak to peak amplitudes as high as 1.0 in. under the influence of a brisk cross wind and heavy traffic. This period agrees well with the calculated period of 4.51 sec (13.31 cpm). Other periods are 2.05 sec (29.27 cpm) and 0.35 sec (171.42 cpm). The cantilever span of extremely stiff design shows a fundamental period of 0.26 sec (231 cpm). The elastic-inertia and aerodynamic characteristics of the Chesapeake Bay Bridge are found to be satisfactory.