The claim is often made that the adoption of single-payer health care in the United States would result in dramatic improvement of services for people with mental health and substance use disorders. Evidence from this sector in countries with such frameworks is mixed, however, presenting both positive and negative lessons for an American audience. Focusing on Canada as an example, this article sheds light on this topic by drawing on sources in the professional and academic literature, government reports, news stories and features, and research on-site by the author. A concluding section highlights key policy issues that American single-payer advocates will need to address for meaningful reform of the behavioral health care sector.