To provide the first systematic test of whether young children will spontaneously perceive and imitate hierarchical structure in complex actions, a task was devised in which a set of 16 elements can be modelled through either of two different, hierarchically organized strategies. Three-year-old children showed a strong and significant tendency to copy whichever of the two hierarchical approaches they witnessed an adult perform. Responses to an element absent in demonstrations, but present at test, showed that children did not merely copy the chain of events they had witnessed, but acquired hierarchically structured rules to which the new element was assimilated. Consistent with this finding, children did not copy specific sequences of actions at lower hierarchical levels.