This paper presents a review of data on the solubility of rare earth oxides in halide melts of alkali and alkaline earth metals. The highest solubility of rare earth oxides is observed in fluoride melts, the lowest – in chloride melts. There are very few works devoted to the study of the solubility of rare earth oxides in mixed chloride-fluoride melts. The solubility of rare earth oxides decreases in the series La-Ce-Pr-Nd-Gd. The greatest number of works are devoted to the study of the solubility of neodymium, lanthanum and cerium oxides. There are practically no data on the solubility of “heavy” rare earth oxides (from Tb to Lu) in halide melts.