This chapter introduces a measure of savoir-faire that represents the abilities required to engage others in interaction and to behave tactfully and successfully in social situations. Drawing on research in nonverbal and social skills, savoir-faire (which translates as “to know (what) to do”) is a combination of abilities in expressing oneself verbally, engaging others in interactions, and sophisticated social role-playing. We assert that savoir-faire represents a core element of social intelligence and that it is associated with social effectiveness, broadly defined. Using data from a self-report measure of social skills, we extracted the measure of savoir-faire. We demonstrate how savoir-faire, so measured, predicts interpersonal behavior in laboratory-based social situations as well as important social outcomes (e.g., likability, breadth of social networks, attainment of leadership positions).