ABSTRACTThere are theoretical debates about the definition of joint attention, and empirical debates about when it emerges in development. Here we addressed both debates by investigating the emergence of infants' communicative joint attention bids: looks to their partner's face, accompanied by communicative facial expressions and/or vocalizations, to attempt to initiate joint attention to a referent. We tested 25 infants monthly, longitudinally, between 6 and 10 months using both novel joint attention elicitation tests and free play observations. Even when using a conservative definition of joint attention involving communication, results indicated that a substantial percentage of infants (44%) had already begun to produce joint attention bids by 6 months, with the vast majority (92%) having done so before 9 months. Joint attention bids emerged gradually, with increasing consistency, and were seen earlier in the novel elicitation tests than in free play, suggesting that previous work focusing on free play might have underestimated infants' joint attention. We discuss the implications of these findings for theories of joint attention and communication.