Colloidal crystallisation is the only way to obtain three-dimensional ordered materials in which semiconductor, metallic, and magnetic nanocrystals are in close contact. It is expected that the quantum mechanical and dipolar interactions between the nanocrystal units can lead to unseen physical phenomena and materials. Here we review the development of this new and exciting field. We first compare nanocrystal superlattices with regular atomic solids regarding their mechanical strength and opto-electronic properties. We describe how nanocrystal superlattices have been obtained from colloid suspensions in several ways. The thermodynamic driving force for colloidal crystallisation is discussed in terms of inter-particle interactions in a good solvent and entropy. We compare the binary superlattices that have been obtained by solvent evaporation with the predictions of the hard-sphere model and show that semiconductor nanocrystals in a good solvent can behave as hard spheres. Finally, we discuss the quantum mechanical and dipolar interactions in nanocrystal superlattices and review recent studies of the opto-electronic and magnetic properties of novel superlattice materials. (C) 2011 Elsevier Ltd. All rights reserved.