Substance use disorder treatment records are governed by a federal confidentiality rule that is older, stricter, and structurally different from ordinary health privacy law, and the difference catches nearly everyone who encounters it. This article explains what Part 2 protects, which programs it applies to, and why the answer turns on how a provider holds itself out rather than on what services it delivers. It explains the consent that Part 2 requires, why an ordinary authorization form is not sufficient, and what the redisclosure prohibition actually does to everyone downstream. It covers the narrow exceptions — medical emergency, qualified service organizations, research, audit, and the court order procedure that is far harder to satisfy than a subpoena. It covers the recent alignment with health privacy law and what did and did not change. It then turns to the surrounding law: parity in insurance coverage, employment and housing protections for people in recovery, the psychotherapist privilege, duty-to-warn doctrine, and the licensing of treatment programs and recovery residences. It closes with what a program must actually build and what a patient should know.