This chapter looks at early interactions between parent and infant, from joint looking at faces, gaze following, and attention to hands and gestures, to later interactions where infants and adults readily capture each other’s attention. It examines the ways adults modify their speech to infants and young children, e.g., with short, grammatical utterances, formulaic routines, repetitions in variation sets, higher pitch, slower rate, and pausing at the ends of utterances. Adults adjust their speech to what their children understand and provide feedback on children’s errors, checking up to make sure they have understood them and so offering them a conventional way to say what they appear to intend. Adults establish joint attention and engage with infant and child activities, anchoring their conversational contributions to what is physically present and visible, and talking about the child’s current activities. And infants become adept at attracting adult attention and enlisting their help in different activities. In child-directed speech, adults focus on what is physically and conversationally present, and respond to the topics children introduce. They choose short, high-frequency words, with high neighborhood density, many with concrete referents present in the here and now. Conversational interactions provide the setting for acquisition.