This article reports a meta-analysis of the effects of the presence of others on human task performance and physiology. In 241 studies involving nearly 24jOOO subjectSj the presence of others had small effects, accounting for .3% to 3% of the variance in the typical experiment. We conclude that (a) the presence of others heightens an individual's physiological arousal only if the individual is performing a complex task; (b) the presence of others increases the speed of simple task performance and decreases the speed of complex task performance; (c) the presence of others impairs complex performance accuracy and slightly facilitates simple performance accuracy, though the facilitation is vulnerable to the file drawer problem of unreported null results; and (d) social facilitation effects are surprisingly unrelated to the performer's evaluation apprehension. These metaanalytic conclusions are contrasted with conclusions reached by narrative literature reviews. Implications for theories of social facilitation are discussed. Since beginning their study of social influence, psychologists have been interested in a minimal source of influence: the mere presence of others. In the first investigation, Triplett (1898) found that adolescents could spin fishing reels more quickly when in coacting pairs than when alone. In other early research, Pessin (1933) discovered that college students made more errors in memorizing nonsense syllables if they learned the syllables in front of a spectator. From such pioneering efforts, a massive research literature grew, a literature that has documented social effects on the performance of myriad tasks. Many researchers (following Triplett, 1898) have found that the presence of others can facilitate task performance; other investigators (following Pessin, 1933) have observed that performance can be impaired by the presence of others. The pres