Research summary: Changing police use of force policies and training to incorporate de-escalation tactics is one of the most routinely recommended police reform measures. Despite widespread promotion and proliferation of de-escalation trainings, to date, no research has empirically demonstrated that these trainings reduce use of force in the field (Engel, R. S., McManus, H. D., & Herold, T. D., 2020). Therefore, it is unknown if de-escalation trainings actually reduce force, have no impact, or have unintended consequences that possibly increase injuries to officers or citizens. We collaborated with the Louisville Metro Police Department (LMPD) in 2019 to evaluate the impact of the Integrating Communications, Assessment, and Tactics (ICAT) de-escalation training developed by the Police Executive Research Forum. Using a stepped-wedge randomized controlled trial research design, the panel regression results demonstrated statistically significant reductions in use of force incidents (−28.1%), citizen injuries (−26.3%), and officer injuries (−36.0%) in the posttraining period. These significant reductions were larger than any changes in LMPD arrest patterns during the