[en] Experimental evidence for the formation of metastable phases in metals using ion implantation is reviewed. Ion channeling and transmission electron microscopy are the main experimental techniques which have been used to investigate these materials. For heavy metallic implanted species at low implanted concentrations (less than or equal to 1 at. percent), the materials are generally substitutional solid solutions, often exceeding equilibrium solid solubilities. At higher concentrations both metastable solid solutions and amorphous structures can be produced. Examples from the Ag : Cu, Ta : Cu, Dy : Ni, and Au : Pt systems are shown to illustrate specific points. A thermal spike-type mechanism has been proposed to explain these behaviors