Modern (theoretical) solid-state chemistry is a most fascinating discipline in that it touches upon many scientific fields. To start with, I will cover how density-functional calculations may pave the way to purely theoretical (first-principles) Gibbs energy data for solids, very much needed to understand and optimize materials of practical interest, e.g., high-temperature superconductors. Such theoretical approaches are also extremely useful when it comes to pre-dicting non-existent compounds of – at the present time – purely academic interest, nicely ex-emplified by high-pressure metal pernitrides, still a very young class of solid-state phases. Likewise, so-called carbodiimides are the nitrogen-analogues of the well-known oxides be-cause here the oxide anion has been replaced by the isolobal carbodiimide anion, very much in the spirit of a “divalent nitride” species; note that such phases have also been made possible only by theoretical reasoning. The entire series of the transition-metal carbodiimides (as op-posed to the chemically less interesting oxides) exhibits unexpected properties such as ferro-magnetism and spin-liquid-like behavior. Finally, salt-like compounds containing the guani-dine species, a biochemically extremely important building block, have recently been predicted and synthesized, and they correspond to the nitrogen analogues of the well-known carbonates. It is clear that the crystal structures of the guanidinates heavily depend on the H-bond network, which often demands theoretical insight from first-principles computations.