The use of any kind of physical force is by far the exception in most police–citizen interactions, and deadly force encounters are rarer still. Police officers use deadly force when they believe they have no choice in order to protect human life—their own or that of other citizens. Any force, however mild or severe, that goes beyond the level necessary to preserve life, prevent injury, or safely control the scene constitutes excessive force. Police officers characteristically restrain their use of force with citizens, sometimes at the cost of their own safety. However, certain types of attitudes, personalities, and job experiences may render some officers more prone to use force in police–citizen encounters, and certain emotional and behavioral features of police–citizen confrontations may eventuate in a tipping point, where force is then deployed. Special circumstances may attend suicide by cop incidents, where disturbed citizens manipulate officers into killing them. Altered patterns of thought and perception often occur in the minds of officers during a deadly force encounter, and the aftermath of such an incident may include both administrative and psychological consequences. Certain racial and ethnic groups—of both police and citizens—may be disproportionately represented in use of force incidents. However, these are mainly related to the demographics of criminal behavior and officer assignment in various communities, and there is no evidence that police systematically target members of certain ethnic groups for more forceful confrontations, unless the situation itself requires it. Certain features of selection, education, training, discipline, and supervision of police officers can help weed out bad cops, improve police–citizen communication, and further reduce the incidence of use of force, including deadly force, encounters.