The Rare Earth Elements (REE) are much more than geochemical tracers. Increasing industrial demands make them important drivers of green technologies. Of their many uses, high temperature magnets and batteries will insure demand increases rapidly over coming decades. The western economies dependent on REE are seeking to diversify source deposits and countries, thus exploration is ramping up. I will review the existing REE deposits and explain their link to peralkaline and carbonatite complexes. I will then discuss features that appear to be hydrothermal and review what we know about REE solubilities in solution and how hydrothermal REE might form. Finally, I will discuss the possibilities of purely hydrothermal REE deposits, review existing models suggest how they may be improved.