Babies in Threes details findings produced by new methods for recording and describing interactions in all-infant trios. These demonstrate that six- to eight-month-olds have capacities for group membership. The chapter uses a detailed analysis of one trio to show that babies can create their own new meanings in the course of infant-only group-interactions. Babies in Threes shows how infants interact with more than one other person at once, combining a multiplicity of resources for multi-directional communication, including: both peripheral and focal vision; sound-making; sharing rhythms; complex combinations of facial expression; touch; gestures; orienting; and imitation. The chapter analyses one twelve-minute group-interaction in detail, paying particular attention to a ‘rude sign’ flicked by one girl at another. This focal event prompts an examination of the potentials and limits of the interpretive processes whereby observers come to assign meanings to or understand behaviours of infants and adults. All such understandings have specific cultural roots.