The application of polymer-based aqueous biphasic systems (ABSs) to the alkaline paper pulping process is reported. ABSs composed of polymers and pulping solution (a mixture of NaOH, Na2S, and Na2CO3) have been characterized. The partitioning behaviors of several model lignin species have been studied in poly(ethylene glycol) (PEG)/pulping solution ABSs over a considerable range of temperatures. Polymer-based pulping experiments containing PEG and polyethylenimine (PEI) performed at different temperatures (130-160 degreesC) indicate that the addition of polymer has a significant effect on the delignification of hardwood. Samples of hardwood chips treated with PEG resulted in a lower kappa number and lower consumption of alkali than those treated with PEI. Polymer-based pulping of hardwood exhibited remarkably faster delignification and 30-60% lower residual lignin content of pulps compared to the control alkali pulping process. At comparable kappa numbers, a 10-20% gain in pulp yield was obtained as a result of the increased selectivity.