The catalytic behavior of several inexpensive and simple N-heterocyclic organic catalysts in ring-opening polymerization (ROP) of ¿-pentadecalactone (PDL) and e-caprolactone (CL) has been studied. The polymerization reactions, carried out in bulk monomer and in toluene solution at 100 °C, identified 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) in combination with benzyl alcohol (BnOH) as initiator as the only active catalyst for the ring-opening polymerization of PDL and for the copolymerization of PDL and CL. The guanidine N-methyl-TBD (MTBD), 1,2,3-triisopropylguanidine, the amidine 1,8-diazabicycloundec-7-ene (DBU), and other N-heterocyclic organic catalysts such as dialkylaminopyridine (DMAP), imidazole, indoles, and N-heterocyclic carbenes (NHC’s) tested in this study proved to be inactive in the ROP of PDL even for the long reaction times. The polymerization mechanism, kinetic studies, temperature, and monomer concentration effects were investigated both in solution and in bulk monomer. The pseudoliving character of the TBD/BnOH system has been proven by kinetic studies in both toluene solution and bulk monomer. By varying the experimental conditions and the monomer feed composition, highly crystalline poly(PDL-co-CL) random copolymers of various compositions have been prepared using the binary system TBD/ROH as catalyst/initiators. Thermal analysis and 13C NMR spectroscopy show a linear relation of the variation of the random copolymers melting temperatures as a function of comonomer content.