A novel and efficient calcium alkoxide initiating system, generated in situ from bis(tetrahydrofuran)calcium bis[bis(trimethylsilyl)amide] and an alcohol, for the ring-opening polymerization of cyclic esters has been developed. The solution polymerization in THF using mild conditions is living, yielding polyesters of controlled molecular weight and tailored macromolecular architecture. The polymerizations initiated with the 2-propanol-Ca[N(SiMe3)(2)](2)(THF)(2) system are first-order in monomer with no induction period. At high 2-propanol/Ca[N(SiMe3)(2)](2)(THF)(2) ratios, complete conversion of a-propanol occurs due to fast and reversible transfer between dormant and active species.