Phase-change materials (PCMs) are widely used for data storage and in other functional devices. Despite their often seemingly simple compositions, these materials exhibit intriguing microscopic complexity and a portfolio of fascinating physical properties. From a more chemical perspective, the technological success of PCMs is a simple consequence of the structural and electronic peculiarities on the atomic scale and, in particular, of their bonding nature. In fact, the chemical bonding of crystalline and amorphous PCMs and also related materials is truly worth studying, now so easily done using state-of-the-art density-functional theory and properly chosen projection techniques as implemented in the Lobster program suite. In addition, finite-temperature properties of such solid-state materials are almost routinely accessible using quasiharmonic theoretical methods from first principles. By doing so, structure-property relationships at zero Kelvin and beyond may be thoroughly analyzed for crystalline and amorphous bulk-like PCMs as well as for surfaces structures, including their oxidation products and chemically related chalcogenides.