For this data collection, information on police-citizen encounters was collected to explore the peacekeeping functions of the police and their handling of encounters with mentally ill persons. The data were gathered for part or all of 270 shifts through observations by researchers riding in police cars in two Chicago police districts during a 14-month period in 1980-1981. In Part 1 (Shift Level), information was collected once per shift on the general level of activity during the shift and the observer's perceptions of emotions/attitudes displayed by the police officers he/she observed. The file also contains, for each of the 270 shifts, information about the personal characteristics, work history, and working relationships of the police officers observed. Part 2 (Encounter Level) contains detailed information on each police-citizen encounter including its nature, location, police actions and/or responses, citizens involved, and their characteristics and behavior. A unique and consistent shift identification number is attached to each encounter so that information about police officer characteristics from Part 1 may be matched with Part 2. There are 1,382 police-citizen encounters involving 2,555 citizens in this collection.