We investigated whether infants comprehend others' nonverbal communicative intentions directed to a third person, in an "overhearing" context. An experimenter addressed an assistant and indicated a hidden toy's location by either gazing ostensively or pointing to the location for her. In a matched control condition, the experimenter performed similar behaviors (absent-minded gazing and extended index finger) but did not communicate ostensively with the assistant. Infants could then search for the toy. Eighteen-month-old infants were skillful in using both communicative cues to find the hidden object, whereas 14-month-olds performed above chance only with the pointing cue. Neither age group performed above chance in the control condition. This study thus shows that by 14-18 months of age, infants are beginning to monitor and comprehend some aspects of third party interactions. (Contains 4 figures and 1 table.)