Recent research has placed one of policing’s most venerable tools—the K9 unit—under fresh empirical scrutiny. The findings of a new study run counter to long-held convictions on both sides of the debate: for decades, one camp has insisted that K9s deter crime, reduce officer harm, and bolster law enforcement’s public image, while the other has contended that K9 deployment leads to undue injury, violates constitutional protections, and perpetuates racial disparities.