This study explores police-citizen encounters and the reaction of each actor to the demeanor of the other throughout the interaction. Police-citizen interactions can be understood as a sequence of events, often changing rapidly and making transitions from being trivial to serious exchanges. The sequence of actions and reactions is designed to support the expectations of both actors. Although the authors understand that these interactions are guided or driven by the actor's needs and abilities to influence, and even coerce, each other, the authors are not clear on the precise definition or role of the actors' demeanor. Most previous research has been limited to a measure of demeanor at one point in time. The authors design allowed for measurement of changes in demeanor as the police-citizen interaction developed, and our examination revealed that the demeanor of both officers and suspects changed during the encounters in a substantial number of cases. Abstract published by arrangement with Sage Journals.