Abstract: Cycloolefin and α–olefin copolymers (COC) with excellent transparency，low dielectric loss，outstanding dimensional stability，high heat resistance and gas barrier property are produced by four companies (Ticona，Nippon Zeon Corp.，JSR Corp. and Mitsui Chemicals) through either ring-opening metathesis polymerization (ROMP) or copolymerization with metallocene catalysts (mCOC). These two routes are compared in respect of catalysts，monomers，production processes and product properties. The COC produced through ROMP route has a larger amount of C—C double bond in the macromolecular chains，therefore it has to go through a hydrogenation process to get rid of 98% of the residual double bond in order to produce high-performance materials. The hydrogenation process is not needed if COC is produced through mCOC route. Consequently，mCOC processes are considered economically favorable compared to ROMP processes.