We report two studies that tested hypotheses about relations between personality, knowledge about service encounters, and performance in service encounters. A novel method for measuring knowledge was used. In one study, we measured undergraduates' personality, knowledge, and skill in handling service encounters in jobs performed by human factors professionals. The other study reanalyzed data reported by Motowidlo, Crook, Kell, and Naemi about volunteers' personality, knowledge about volunteer service encounters, and job performance. Both studies found that knowledge about service encounters is correlated with effectiveness in service encounters, even when effects of personality are controlled. Conscientiousness was correlated with this knowledge. We discuss implications of personality in the development of knowledge about effective behavior in social situations at work.