Microchannel devices were designed and tested for efficient contacting of two liquids in solvent extraction, and the results are presented. This study is part of an overall effort to produce and demonstrate efficient compact devices for chemical separations. Engineering these devices at the microscale offers many technical advantages. Achieving high contact area per unit system volume, thin-film contacting, and establishing uniform flow distribution result in substantially higher throughput per total system volume over conventional technologies. Theoretical calculations are presented that provide insight into the relative importance of various resistances to mass transfer, as well as their relationship to overall performance of the microchannel devices. Experimental results are presented for device performance using both commercial polymeric membranes and micromachined contactor plates for stabilizing the liquid-liquid interface. These results indicate that current-generation micromachined plates perform as well as commercial membranes, with substantial potential for improvement.