Police discretion has large potential consequences for public trust and safety; however, little is known about the extent of this discretion. I show that arrests critically depend on which officer responds to a 911 call; 1 standard deviation increase in officer arrest propensity raises arrest likelihood by 40%. High arrest officers are more likely to be white and have less experience. I find mixed evidence that arrest propensity is related to arrest quality. High arrest officers use force more often and make more low-level arrests, while they also have a higher share of low-level arrests that result in conviction.