A range of ring-opened metathesis copolymers of norbomene and cyclopentene have been prepared and "C NMR spectroscopy used to analyse in detail the nature of the homo and heterodyad units. This has provided significant new information on the sensitivity of the [2 + 21 cycloaddition step in metathesis to the steric and electronic factors associated with the [Mt]=C and C=C moieties involved. Novel very high cis directing catalyst systems, have also been developed for the homopolymerization of norbomene using various ethers with MO and W-based catalyst systems or chelating dienes and phenylacetylene with RuCl, and OsCl, systems. The general feature of cis/tmns blockiness at high cis content is investigated in much greater detail. A clearer description of the associated relaxation processes of the propagating species emerges from this work. The metathesis polymerization of the matched pair, benzonorbomadiene and 7-oxa-benzonorbornadiene has been investigated using Ru and OS-based initiators. The results illustrate the subtle way whereby the presence of the proximate 'I-O-atom may facilitate [2 + 21 cycloadditions. This constitutes a valuable novel method of studying key electronic factors in the mechanism of the metathesis reaction.