The Mental Health Justice Act of 2023 would provide $250 million in federal grants over five years to states, tribes, and local governments to hire and train mental health professionals who respond to certain 911 calls instead of police officers. These mental health responders would handle emergencies involving people in mental health crises, those with mental illness or developmental disabilities, or individuals appearing to be under the influence of substances, and would include training in deescalation techniques and connections to community services. The bill gives funding priority to areas with high rates of arrests and incarceration of people with mental health conditions and requires grantees to submit quarterly reports on how many emergencies mental health professionals respond to and whether the programs reduce incarceration and institutionalization. The law includes safeguards allowing police to continue responding to dangerous situations and requires the federal government to study program effectiveness within three years and develop best practices for deploying mental health first responders.