Soybean aphid (SA) was first found in the northern soybean growing regions of the USA in 2000. By 2005, the aphids have spread to 23 soybean growing states reaching as far south as Mississippi and Georgia and covering nearly 80% of soybean, Glycine max (L.) Merr., fields in the country. The objective of this study was to identify new sources of resistance to the SA. More than two hundred soybean lines (cultivars, breeding lines and plant introductions) were evaluated by choice tests for resistance to soybean aphids in a greenhouse. Three soybean plant introductions (PIs) were identified as highly resistant against the soybean aphids. The resistance of these PIs was confirmed in the field and greenhouse by further choice and non-choice tests. Mapping populations and backcross breeding lines have been developed by crossing these resistant PIs to elite cultivars.