The conventional anionic polymerization of propylene oxide (Pox) proceeds at a very slow rate in low polar media and is characterized by an important transfer. reaction to monomer. This only allows the formation of poly(propylene oxide) oligomers. A new p olymerization strategy allowing the fast and controlled anionic polymerization of Pox has been developed. It is based on the formation of complexes with both the anionic initiator and the monomer. The influences of alkali metal alkoxides (i-PrONa), ammonium salts (NBu4Cl and NOct(4)Br), and phosphonium salts (PBu4Cl) as initiators, in combination with triisobutylaluminum, have been investigated in terms of reactivity, molar mass control, livingness, and polymerization mechanism. PPOx with narrow polydispersities and controlled molar masses, up to 150 000 g/mol, have been obtained in hydrocarbon media, at low temperature, and in short reaction times.