Alcoholics Anonymous (AA) is an international peer-led mutual aid fellowship meeting online and in-person dedicated to abstinence-based recovery from alcoholism through its spiritually-inclined Twelve Step program. Following its Twelve Traditions, AA is non-professional and non-denominational as well as apolitical and unaffiliated. In 2020 AA estimated its worldwide membership to be over two million, with 75% of those in the U.S. and Canada.

Although AA holds no opinion on the disease model of alcoholism—or on any medical issue, many AA members took a large role in making it popular. Regarding its effectiveness, a 2020 scientific review saw clinical interventions encouraging increased AA participation resulted in higher abstinence rates over other clinical interventions for alcohol use disorder, and most studies in the review found that AA led to lower health costs.

AA dates its start to 1935 with Bill Wilson (Bill W) first commiserating alcoholic to alcoholic with Bob Smith (Dr. Bob) who, along with Wilson, was active in AA's immediate precursor the Christian revivalist Oxford Group. Within the Oxford Group, Wilson and Smith joined other alcoholics in supported each other in meetings and one on one until breaking off to form a fellowship of alcoholics only. In 1939 they published Alcoholics Anonymous: The Story of How More Than One Hundred Men Have Recovered From Alcoholism. Known as the "Big Book" and as the source of AA’s name, it contains AA's Twelve Step recovery program. Subsequent editions included the Twelve Traditions adopted in 1950 to formalize and unify the fellowship, which Wilson called “a benign anarchy”.

The Twelve Steps are presented as a continuing suggested self-improvement program leading to a spiritual awakening after an alcoholic has conceded powerlessness over alcohol and acknowledged its damage, as well as having listed and strived to correct personal failings and by making amends for misdeeds. After completing the Steps they suggest members take other alcoholics through them. Though not explicitly prescribed, this is often done by sponsoring other alcoholics. Divining and following the will of God—"as we understood Him"— is also urged by the Steps, but differing spiritual practices and persuasions, as well as non-theist members, are accepted and accommodated.

The Twelve Traditions are AA's advisory guidelines for members, groups and the rest of its organization. Besides making a desire to stop drinking the only membership requirement, the Traditions advise against dogma, hierarchies and involvement in public controversies to preserve recovery from alcoholism as AA’s primary purpose. Without threat of retribution or means of enforcement, the Traditions urge members to remain anonymous in public media. They also wish members or groups to not use AA to gain wealth, property or prestige. The Traditions establish AA groups as autonomous and self-supporting through members’ voluntary contributions while rejecting outside donations, and, as with all of AA, should not represent AA as affiliated with or in support of other organizations or causes.

With AA's permission, other fellowships such as Narcotics Anonymous and Al-Anon have adopted and adapted the Twelve Steps and the Twelve Traditions to their addiction recovery programs.