In contrast to the case of gravity-dominated buildings, the seismic design process has to consider all structural components which transfer horizontal loads to the foundation soil. They can be grouped in three main, relatively homogeneous, components constituting the building structural system: (a) superstructure (currently called structure), (b) infrastructure and/or foundations, and (c) foundation soil. Within the present chapter it is pointed out that the consideration of the mutual interaction of these three components as well as an organized whole is of crucial importance in correct determining and understanding of the seismic building response. Most commonly used reinforced concrete structures for multistory buildings are compared and their optimum usage domain is specified.