Conventional finite-element-based structural shape optimization requires the calculation of grid sensitivities which are much more expensive to compute than size sensitivities. This thesis presents a new method of shape optimization which is based on using size sensitivities to guide shape redesign. In this method a thin layer of plate elements is cast on selected free surfaces of structures modeled with solid elements, or in the case of structures modeled with plate elements, selected free edges are covered with a thin lining of beam elements. While the performance of the structure remains virtually unaffected by introducing these nearly zero section elements, the sensitivities of the structural response with respect to the thickness of these elements provide valuable insight on the behavior of the structure. Methodologies for using these sensitivities to optimize the shape of structures are introduced. Applications to several case studies involving displacement, stress, and frequency response variables are presented.