In general, pile materials are assumed to be isotropic during the analysis of the load}de#ection response of piles under lateral loads. However, commonly used materials such as reinforced concrete and timber as well as potentially promising new pile materials such as "ber reinforced polymers are typically transversely isotropic materials. Experimental studies have shown that transversely isotropic materials have a high ratio of section longitudinal modulus to the section in-plane shear modulus (E XX /G VX ) compared to the value for isotropic materials. The high modulus ratio leads to a more signi"cant shear deformation e!ect in beam bending. To account for the shear deformation e!ect, the Timoshenko Beam Theory has been adopted in deriving the solutions for the load}de#ection response of transversely isotropic piles under lateral loads instead of the Classical (Euler}Bernoulli) Beam Theory. The load}de#ection responses depend on the shear e!ect coe$cient, the lateral soil resistance, the embedment ratio, and the boundary conditions. The de#ection of the pile, if the shear deformation e!ect is considered, is always larger than if it is neglected.