This chapter provides an overview of mutual-help groups for Affected Others (family and friends affected by, or concerned about, someone else’s alcohol or other substance use). The overview covers the major types of mutual-help groups for Affected Others: 12-step and non-12-step, also known as 12-step alternatives. Then, the chapter turns to examining research on outcomes of Affected Others’ participation in mutual-help groups, such as their understanding of alcohol use disorders, mental health symptoms, coping skills, and relationship functioning. Because Al-Anon Family Groups (Al-Anon) is the mutual-help group with the largest knowledge base, it is the focus of this examination of participation outcomes. The chapter also examines associations of Affected Others’ participation in mutual-help groups with recipients’ (the persons with alcohol or other substance use) outcomes, such as their abstinence and own participation in mutual-help groups. Because Al-Anon has been shown to be beneficial to Affected Others, the chapter describes mechanisms through which Al-Anon helps members and considers these mechanisms in the context of different cultures. These mechanisms include the group’s support, encouragement of personal growth, provision of norms and role models, and bolstering of coping skills. Finally, in light of findings that the combination of professional treatment with Al-Anon participation may be particularly helpful to Affected Others, the chapter closes with suggestions for healthcare providers to refer Affected Others to Al-Anon or another mutual-help group.