A series of experiments is reported which show that three successive mechanisms are involved in the first 18 months of life in ‘looking where someone else is looking’. The earliest ‘ecological’ mechanism enables the infant to detect the direction of the adult's visual gaze within the baby's visual field but the mother's signal alone does not allow the precise localization of the target. Joint attention to the same physical object also depends on the intrinsic, attention‐capturing properties of the object in the environment. By about 12 months, we have evidence for presence of a new ‘geometric’ mechanism. The infant extrapolates from the orientation of the mother's head and eyes, the intersection of the mother's line of sight within a relatively precise zone of the infant's own visual space. A third ‘representational’ mechanism emerges between 12 and 18 months, with an extension of joint reference to places outside the infant's visual field.None of these mechanisms require the infant to have a theory that others have minds; rather the perceptual systems of different observers ‘meet’ in encountering the same objects and events in the world. Such a ‘realist’ basis for interpersonal knowledge may offer an alternative starting point for development of intrapersonal knowledge, rather than the view that mental events can only be known by