“…Whereas CL and MMA have been, at the early stage, the most studied monomers, other polar as well as nonpolar monomers have been considered next, especially lactones (b-propiolactone (PL), VL), carbonates (trimethylene carbonate (TMC), dimethyl-TMC), oxiranes (ethylene oxide, propylene oxide, epichloridrin), alkyl (methyl, ethyl, isopropyl, t-butyl) (meth)acrylates, as well as olefins (ethylene, 1-hexene, styrene), conjugated dienes (butadiene, isoprene), or acetylene derivatives. The latest Chapter 259 Rare-Earth Borohydride Complexes in Polymerization contributions, in particular from Hou (Hou and Nishiura, 2010;Hou and Wakatsuki, 2002;Hou et al, 2006), Endo (Nomura and Endo, 1998), Agarwal and Greiner (Agarwal and Greiner, 2002;Agarwal et al, 2000), Kerton (Kerton et al, 2004), or Edelmann (Edelmann, 2009(Edelmann, , 2010(Edelmann, , 2011, have addressed more specific domains. Following the developments in organometallic synthesis of rare-earth complexes, original neutral or cationic initiators, either monoor bicomponent catalytic systems, showed novel activity and regio-and/or stereo-selectivity in (co)polymerization; these include half-metallocene complexes bearing mixed Cp*-monodentate anionic ligands or cyclopentadienyl (Cp)-amido and -phosphido linked ligands, as well as Cp-free complexes such as [(COT)RCl] (COT ¼ cyclooctatetraenyl).…”