The ring-opening polymerizations (ROPs) of epsilon-caprolactone (epsilon-CL) and delta-valerolactone (delta-VL) with pentafluorophenyl-bis(triflyl)methane (C(6)F(5)CHTf(2)) as the organocatalyst and alcohol initiators were carried out. For the ROP using 3-phenyl-1-propanol (PPA) as the initiator in CH(2)Cl(2) at room temperature with the [epsilon-CL or delta-VL](0)/[PPA](0)/[C(6)F(5)CHTf(2)] ratio of 50/1/0.1, the polymerization homogeneously proceeded to afford poly(epsilon-caprolactone) (PCL) and poly(delta-valerolactone) (PVL) having narrow polydispersity indices. The molecular weights of the obtained polymers determined from (1)H NMR spectra showed good agreement with those estimated from the initial ratio of [epsilon-CL or delta-VL](0)/[PPA](0) and monomer conversions. The (1)H NMR, size exclusion chromatography, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry measurements strongly indicated that PCL and PVL possessed the 3-phenylpropoxy group as the alpha-chain-end and the hydroxy group as the omega-chain-end. In addition, the controlled/living nature for the C(6)F(5)CHTf(2)-catalyzed ROP of lactones was confirmed by kinetic and chain-extension experiments. The block copolymerization of PCL and PVL successfully proceeded to afford PCL-b-PVL and PVL-b-PCL. In addition, various end-functionalized PCLs and PVLs with narrow molecular weight distributions were synthesized by the ROP of epsilon-CL and delta-VL using functional initiators, such as 6-azido-1-hexanol, 2-hydroxyethyl methacrylate, propargyl alcohol, N-(2-hydroxyethyl)maleimide, 4-vinylbenzyl alcohol, 5-hexen-1-ol, and 5-norbornene-2-methanol. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3769-3777, 2011