Humans may run faster, read less or type more quickly, simply because someone else is present. The presence of one person affects the behaviour of another: this is known as social facilitation and is one of the oldest topics in social psychology. Despite its importance this was the first book-length study of the phenomenon when it was published in 1993. Dr Guerin reviewed all work in the area from 1898 onwards, looking at both animal and human research, and developed his own theory, based on modern behaviour analysis. The book will be appreciated for its wide-ranging and balanced review of previous work on social facilitation and for the general review of the state of social psychology during the 1990s that Dr Guerin's work on the phenomenon includes. The author's theoretical stance is innovative and important, and will make the work required reading.