This book presents the development of a new method to predict load-deformation responses of reinforced concrete (RC) columns both with and without fiber reinforced polymer (FRP) jacketing under seismic loading. In the case of the flexure mechanism, the section analysis was applied considering the confinement effect of FRP jacketing. This section analysis was combined with the shear mechanism, which was modeled based on the truss mechanism. The flexure-shear models showed significant interactions due to the reduction of reinforcement secant stiffness after yielding and concrete deterioration. The analytical method was verified using an experimental program consisting of square columns strengthened with FRP-jacketing that was tested under reversed cyclic loading, and various parameters including steel reinforcement and fiber ratio were investigated. The proposed analytical method is more effective for predicting the load-deformation relationship, including the post-peak behavior of FRP-jacketed RC columns, than the conventional analytical method and proves that fibers with high fracture strain can provide good ultimate ductility.