Phosphorus ylides are not only classical reagents in organic chemistry, but also play an increasingly important role as novel components in organometallic compounds. These metallic “ylide complexes” are either synthesized from “preformed ylides” and coordination compounds by addition or substitution, on the building block principle, or they are formed, in sometimes complicated reactions, from phosphanes, metal complexes, and C1 substrates in the coordination sphere of the metals. The resulting metal-carbon bonds are greatly modified in their properties by the immediate presence of the phosphonium center and often belong to the most stable of M-C structural units. The metal can come from any group of the periodic table, including the lanthanoids and actinoids. Numerous preparative and structural studies are gradually enabling us to gain an overall picture of the scope of this area of research.