Reactivity of the rare earth metals towards the different elements is described. Comments are mainly made on the thermodynamic data relevant to the formation of the binary compounds and to their trends. The different behaviour of the trivalent rare earths and of europium and ytterbium is underlined. An indication is also given for a few reactions involving more complex reagents or compounds. Comments are finally made on the use of the reported data in the discussion of the preparation and handling methods of the rare earth metals and of their alloys.