Nanostructured materials have been extensively studied for more than 10 years because of tremendous potential to application in a variety of technology, such as electronics, materials science, and biotechnology. Although a large part of these studies concerns nanostructures in three dimensions, this section focuses on nanostructures in rather lower dimensions, on solid surfaces. Moreover, “nano-” usually means the range of a few to hundreds of nm; however, we concentrate on the structures one order smaller than usual, in other words, the structures in “atomic scale” rather than “nanometer scale,” especially those formed on well-characterized surfaces under ultrahigh vacuum (UHV) conditions. Even in this scale, nanostructures can be formed both by selforganization and by ultrafine machining. Before we present our latest studies, some categories of this kind of nanostructures are introduced in this section. We do not attempt to present a detailed review with reference to huge number of articles, but give a few examples of each category with emphasis on the initial works or fundamental studies.