Publisher Summary This chapter describes how ring-opening polymerization (ROP) processes offer the attractive advantage that they generally proceed via a chain-growth mechanism. Therefore, these processes are not subject to the stringent stoichiometry and conversion requirements which usually impede the preparation of high molecular weight polymers via condensation routes. The use of metal-containing monomers of this type usually makes the assurance of exact stoichiometries during condensation polymerization reactions virtually impossible and therefore leads to the formation of low molecular weight oligomers rather than more desirable high molecular weight materials. The molecular weights of 1400–7000 reported for these materials are characteristic of condensation processes where exact reaction stoichiometries are virtually impossible because one reactant, in this case dilithioferrocene, cannot be readily prepared in pure form. One of the well-examined characteristics of the ferrocene nucleus is its ability to undergo a reversible one-electron oxidation. Polymers such as poly (viny1ferrocene) possess electroactive ferrocenyl moieties which are well-separated from one another by insulating organic units.