Rare‐earth halides may be reduced by rare‐earth metals (conproportionation) and, as an alternative, by unlike metals such as alkali or alkaline‐earth metals, a route first established for the production of rare‐earth metals. It has great power for exploratory research subject to enhanced reactivity at lower temperatures and the formation of alkali halide flux for crystal growth. A large number of new compounds, ternary and higher, salt‐like and (semi‐)metallic including interstitially stabilized cluster compounds has been synthesized and characterized during the last decades.