When a person begins to speak, the motions of the respiratory system, vocal folds, and articulators are coordinated through relatively large excursions in a small window of time. As the pressure drive for creating a sound source is established and the articulators move appropriately for the initial sound segment, acoustic cues are generated that form the set of prosodic cues associated with the start of an utterance. The principles underlying variation in these acoustic cues could be better quantified given additional data on the coordination of the respiratory system actions. In this chapter, net muscular pressures from Campbell diagrams are analyzed for normal read speech in American English. As a speaker starts talking, the respiratory system executes a rapid and large change in net muscular pressure with very little volume change. Utterance onset generally begins during net inspiratory muscular pressure - prior to the point at which the respiratory system has generated a ‘relatively constant working level’ for alveolar pressure. A limited number of pauses within a breath group (silent and filled) are examined, and all show a distinct change in the momentum of the respiratory system. Respiratory system involvement is present for various types of sound segments at the pause as well as various locations of pauses within the utterance.