Two studies were conducted to investigate how 14- to 16-month-old infants select actions to imitate from the stream of events. In each study, an experimenter demonstrated two actions leading to an interesting effect. Aspects of the first action were manipulated and whether infants performed this action when given the objects was observed. In both studies, infants were more likely to imitate the first action when it was physically necessary to generate the effect, and in Study 2 they were also more likely to imitate the action when it was socially cued. It seems that infants' own knowledge of space and causality as well as their sensitivity to others' social signals both contribute to their tendency to imitate actions.