Aliphatic diols and dicarboxylic acids condense in hydrophobic solvents to form polyesters at 27-75 degrees C when the solutions interface with an acidic hydrophilic phase. Certain aliphatic omega-hydroxy acids behave similarly. Rigorous removal of the by-produced water by distillation is unnecessary and examples are cited where polyesters are isolated in 85-90% yields having number-average molecular weights between 10,000-35,000. Polydispersity indices tend in many cases to be lower than expected for statistical step-growth polymerizations. Many of the side reactions encountered in high temperature polyesterifications, depending on the nature of the acidic phase, are absent or suppressed. While there are some limitations on the type of monomer, the mild conditions offer the possibility of forming polyesters with temperature sensitive structures directly from the corresponding carboxylic acids and carbinols.