Two studies were conducted to examine the bases for age differences in the construction of social inferences. In each study, adults aged from 20 to 80 years were presented with an impression formation task in which they first read brief behavioral descriptions of fictitious people and then made a trait inference and likability judgment about each person. Results were generally consistent with previous findings in showing that aging was associated with an increase in the weighting of trait-diagnostic information in making trait attributions. In addition, the pattern of age effects was only minimally affected by situational factors that have been known to influence the use of trait-diagnostic information. The findings are interpreted as demonstrating an aging-related increase in social expertise in which knowledge regarding the underlying bases for the behaviors of others has been translated in specific procedural knowledge.