The self-assembly of functionalized nanoparticles (NPs) into colloidal superlattices is attracting great interest. A wide range of supramolecular architectures can be obtained by guiding the self-assembly of the NPs toward various types of crystalline or quasicrystalline aggregates. Crystalline NP superstructures have been attained, for example, via rational design of NP shape, anisotropy, surface chemistry, or by manipulating the conditions of the self-assembling process. Another effective way to control the formation of ordered colloidal superlattices is to use molecular binding units capable of driving NP self-assembly. As an example, the specific recognition between complementary DNA strands grafted onto the NP surface has been used to assemble, with great precision and fidelity, colloidal NP superlattices with various symmetries and fascinating properties. Electrostatic interactions have been also widely employed to drive the self-assembly of colloidal particles. For example, the co-assembly of oppositely charged NPs or the self-assembly of same-charge colloidal entities using oppositely charged binders or ions has allowed to generate binary crystals, homo-NP superlattices, or supramolecular fibers among other materials. While the NP structure, the NP-NP interactions, self-assembly process, and NP organization in the supercrystals are crucial factors for the properties of these materials, in the case of mediated self-assembly it has been demonstrated how the nature and behavior of the mediating species is also of key importance. On the one hand, such supramolecular materials are interesting for their fascinating properties (among others, plasmonic, magnetic, and electrical). On the other hand, from a fundamental point of view, NP superlattices are perhaps even more intriguing, as they represent to some extent larger-scale analogs of atomic crystals, where the NPs organize in space as "superatoms". In general, learning how to master the interparticle interactions in such a way as to obtain colloidal supercrystals with controllable higher-scale features is a major goal. However, the atomic/molecular factors underpinning the emergence of collective assembly properties often remain difficult to ascertain.