This review tries to establish what is the current understanding of the rare-earth monopnictides and monochalcogenides from first principles. The rock salt structure is assumed for all the compounds in the calculations and wherever possible the electronic structure/properties of these compounds, as obtained from different ab initio methods, are compared and their relation to the experimental evidence is discussed. The established findings are summarised in a set of conclusions and provide outlook for future study and possible design of new materials.