Joint speech includes chanting, singing in unison, swearing public oaths, hollering at political rallies, and the humble ritual of singing “Happy Birthday”. It is found wherever people speak or sing the same words at the same time. This familiar behavior is found in prayer and ritual, in protest, on the football terraces, in classrooms, and in many other situations of note. These occasions are considered highly significant to those who take part, and yet joint speech has not been addressed from a scientific or linguistic perspective until now. This book provides a broad framing of how we might study joint speech. It explores topics in linguistics, movement science, neuroscience, and beyond, but it does not assume the reader is at home in any of these. Rather, joint speech is familiar to us all, and the discussion here leads to a broader consideration of how we understand our collective nature. The topic provides an opportunity to address the difficulties and opportunities we encounter in considering collective subjects, collective meaning-making, and collective identities. Joint speech thus opens the door to a renewal of the human sciences in which we are not merely individuals, but are grounded in collectives of many kinds.