The purpose of the present study was to identify common stressors and the magnitude of stress reactivity in police officers during the course of general duty police work. Using heart rate as a primary indicator of autonomic nervous system activation, coupled with observed physical activity data collected through 76 full shift ride-alongs, this study differentiates between physical and psycho-social stress. The results, confirming previous research based on self-report data alone, demonstrate that police officers experience both physical and psycho-social stress on the job, anticipating stress as they go about their work, while suffering anticipatory stress at the start of each shift. The results demonstrated that the highest levels of stress occur just prior to and during critical incidents, and that officers do not fully recover from that stress before leaving their shift. Overall, the results illustrate the need to consider stress reactivity and repressors in the assessment of police officer stress while clearly demonstrating the need for debriefing after critical incidents and increased training in stress management and coping strategies. Taken as a whole, research on policing and stress suggests that police work is in fact stressful. As Anshel (2000), citing others, reminds us, it is one of the most stressful occupations in the world. We also know that stress, particularly when it becomes chronic, can lead to a multiplicity of problems for the officers as well as for the organization they work for. For example, the literature on police officer stress indicates that stress can lead to a greater likelihood of absenteeism, burnout, job dissatisfaction, early retirement or attrition, a weakened immune system with increased shortand long-term illness, long-term disability, poor work performance, and potentially, premature