Near the time of Natta’s discovery of stereoselective alkene polymerization, Baggett and Pruitt1-3 reported that iron (III) chloride was capable of forming poly(propylene oxide) that could be divided into amorphous as well as crystalline materials using solvent fractionation.4 Soon thereafter, Natta et al.5 and Price et al.6,7 provided evidence that the crystalline material was isotactic poly(propylene

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oxide), in which the main-chain methyl substituents were of the same relative configuration. This finding marked the first discovery of a stereoselective catalyst for epoxide polymerization. Since that time, significant advances have been made in stereoselective epoxide polymerization, which is the topic of this chapter.