We propose that the atomically controlled nanostructures and heterointerfaces should be one of the best places to realise the materials design from the viewpoint of the electron correlation, as theoretically demonstrated here for ferromagnetism, superconductivity from three examples with first-principles calculations: (i) a purely organic polymer of five-membered rings, for which the flat-band ferromagnetism due to the electron-electron repulsion is proposed, (ii) metal-induced gap states of about one atomic layer thick at insulator/metal heterointerfaces, recently detected experimentally, for which an exciton-mechanism superconductivity is considered, (iii) an alkali-metal doped zeolite, a prototypical nanostructured host-guest system, for which we propose a picture of the "supercrystal" comprising "superatoms" to examine Mott-insulator and magnetic properties. These indicate that the design of electron correlation is indeed a promising avenue for nano- and hetero- structures. (C) 2004 Elsevier B.V. All rights reserved.