Conventional aircraft wing structures consist of skins over a network of substructures and stiffeners that are approximately straight and orthogonal (ribs and spars). New manufacturing techniques such as additive manufacturing, Electron Beam Free Form Fabrication, Friction Stir Welding, and other variants have dramatically changed the cost-complexity tradeoff, and have made it worthwhile to consider the case where the underlying structure is not made of straight, regular members. The introduction of curvilinear spars and ribs (SpaRibs) has the potential to significantly increase performance, especially where the possibility of a fine tailoring of stiffness axes is beneficial, such as buckling and aeroelasticity. This paper describes a set of tools and techniques for defining, modeling, analyzing, and optimizing aircraft structures with SpaRibs, and begins to investigate the resulting performance benefits.