When involved in face-to-face conversations, people move their heads in typical ways. The pattern of head gestures and their function in conversation has been studied in various disciplines. Many factors are involved in determining the exact patterns that occur in conversation. These can be explained by considering some of the basic properties of face-to-face interactions. The fact that conversations are a type of joint activity involving social actions together with a few other properties, such as the need for grounding, can explain the variety in functions that are served by the multitude of movements that people display during conversations. 1