Publisher Summary A shaft is a structural member that is used to transmit power as well as rotational motion. This chapter focuses on the analysis of a determinate shaft of simple geometry that is subjected only to torque. The stress and deformation in a shaft are primarily because of the applied torque because temperature and support settling have little effect. Temperature does not change the response because no shear strain is induced in a shaft made of an isotropic material. Settling of the support of a shaft, which represents a slippage at the boundary, induces a uniform rigid body rotation throughout its length. Because of the circular symmetry, this rotation is inconsequential, except that it changes the reference to measure the angle of twist without any change to the angle itself. The analysis is for the applied torque load, and it is introduced in stages that included the analysis of internal torque, torsion formula, and deformation analysis. Deformation analysis establishes the relationship between the angle of twist and the shear strain.