Body-worn cameras (BWCs) have become increasingly common in U.S. police departments, but we know little about their use in the field, including the factors related to whether and why police activate them. A new study examined the prevalence and correlates of BWC activation in Phoenix, Arizona. The study found that departmental policy may be the most important factor in determining BWC activation, and that policies that confine, structure, and check officers' activation of BWCs affect officers' decisions about turning on the devices.