The work analyses the head nod, a down-up movement of the head, as a polysemic social signal, that is, a signal with a number of different meanings which all share some common semantic element. Based on the analysis of 100 nods drawn from the SSPNet corpus of TV political debates, a typology of nods is presented that distinguishes Speaker’s, Interlocutor’s and Third Listener’s nods, with their subtypes (confirmation, agreement, approval, submission and permission, greeting and thanks, backchannel giving and backchannel request, emphasis, ironic agreement, literal and rhetoric question, and others). For each nod the analysis specifies: 1. characteristic features of how it is produced, among which main direction, amplitude, velocity and number of repetitions; 2. cues in other modalities, like direction and duration of gaze; 3. conversational context in which the nod typically occurs. For the Interlocutor’s or Third Listener’s nod, the preceding speech act is relevant: yes/no answer or information for a nod of confirmation, expression of opinion for one of agreement, prosocial action for greetings and thanks; for the Speaker’s nods, instead, their meanings are mainly distinguished by accompanying signals.