This guide covers involuntary mental health treatment from the first emergency hold through discharge, review, and the collateral consequences that follow. It sets out the constitutional framework the Supreme Court has built around civil confinement, the statutory elements every state adds to it, and the difference between the custody question and the treatment question that practitioners conflate constantly. It explains emergency holds and their clocks, the substantive standards of dangerousness and grave disability, the clear and convincing evidentiary burden, and the procedural rights that attach at a commitment hearing. It covers the separate law of refusing medication, the conditions-of-confinement standard, restraint and seclusion, and commitment of minors. It then addresses assisted outpatient treatment, the integration mandate, and the three criminal-adjacent commitment regimes that are governed by different rules. It closes with review, release, habeas, damages, records, firearms relief, and the practical work of representing a respondent.