The term “model polymers” has long been utilized to designate linear macromolecules of controlled size and low dimensional fluctuation. Interest in these polymers was mainly motivated by the need for samples of well-controlled length, useful for the calibration of characterization techniques such as viscometry and size exclusion chromatography. Methods based on “living” polymerizations—so called because of the absence of transfer and termination reactions-proved to be the best suited for this objective. The first example of such a process was given by Szwarc [1, 2], who demonstrated that the anionic polymerization of styrene is free of the above-cited side reactions, when carried out in aprotic solvents. From the observation made while carrying on this study, Szwarc invented the concept of “living” polymerization. Since this pioneering work, many other unsaturated and heterocylic monomers have been shown to undergo “living” polymerizations through one of these five processes: anionic [3–6], cationic [7–9], metathesis [10–12], group transfer [13, 14], and even free radical [15–17]. This has led to a noticeable diversification of tailor-made linear polymers.