Two different methodologies for the synthesis of monotelechelic poly(oxa)norbornenes prepared by living ring-opening metathesis polymerization (ROMP) are presented. The First met hod, termed direct end-capping, is carried Out by adding an internal cis-olefin terminating agent (TA) to the reaction mixture immediately after the completion of the living ROMP reaction. The second method relics oil cross-metathesis (CM) between a methylene-terminated poly(oxa)norbornene and a cis-olefin TA mediated by the ruthenium olefin metathesis catalyst (H(2)IMes)(Cl)(2)Ru(CH-o-OiPrC(6)H(4)) (H(2)IMes = 1,3-dimesitylimidazolidine-2-ylidene). TAs containing various functional groups, including alcohols, acetates, bromides, alpha-bromoesters, thioacetates, N-hydroxysuccinimidyl esters, and Boc-amines, as well as fluorescein and biotin groups, were synthesized and tested, The direct end-capping method typically resulted ill > 90% end-functionalization efficiency, while the CM method was nearly as effective for TAs Without polar functional groups or significant steric bulk. End-functionalization efficiency values were determined by H-1 NMR spectroscopy.