The first part of this study is a description and analysis of experimental investigations conducted to determine the nonlinear stress-strain behaviors of uniform sands when subjected to cyclic loadings at small strain levels. A series of torsional shear tests are performed under undrained conditions to analyze the variations in the stress-strain properties of saturated uniform sands consolidated to specified confining stresses and with certain relative densities. The role of effective confining pressure on the cyclic properties of isotropically consolidated sands is also considered. The second part of the study uses nonlinear multiple regression, neural network, and adaptive neuro-fuzzy inference methodologies to identify the complex mappings that range from void ratio and confining pressure input spaces to dynamic shear modulus output space. Test results and model comparisons are presented and evaluated in detail.