This handbook is designed for anyone concerned about a person with mental illness who is involved in the New York City (NYC) criminal justice system. It describes the steps an individual goes through following arrest in New York City, from appearance at the local precinct house to central booking, the "court pens," meeting with a defense attorney, arraignment, and going to jail. The paper includes telephone numbers and websites for various NYC law enforcement entities and mental health organizations and where to obtain further information, describes Orders of Protection, and reviews the public defender program. It also describes laws relating to defendants with mental illness; "730 exams" to determine whether a defendant is competent to assist in his/her own defense; the "not guilty by reason of insanity" defense; advocating for a defendant to be sentenced to treatment, for discharge planning, or for someone on probation or parole. The paper briefly discusses stopping the criminalization of mental illness. Glossary, notes