The presence of one person affects the behavior of another: this is known as social facilitation. It is one of the oldest topics in social psychology, first studied in 1898, yet Bernard Guerin's is the first book-length study of the phenomenon. Dr. Guerin reviews all work in the area from 1898 onward, looking at both human and animal research, and develops his own theory, based on modern theory analysis. Through his study of social facilitation, he also reviews the state of social psychology today: its strengths, its weaknesses, and its future.