Living ring-opening metathesis polymerization of cyclopentene, initiated with a well-defined tungsten alkylidene complex, has been used to prepare low polydispersity linear and star poly(1-pentenylene)s. This was achieved by using di- and trifunctional aldehydes in the Wittig-like capping reactions of the living polymers. The resulting materials were hydrogenated to the corresponding polyethylene structures using a from p-toluenesulfonyl hydrazide. An overview of this process, together with characterization data for the resulting materials, is presented.