The Aryan Brotherhood (AB or The Brand) is a neo-Nazi prison gang and an organized crime syndicate that is based in the United States and has an estimated 15,000–20,000 members both inside and outside prisons. The Southern Poverty Law Center (SPLC) has characterized it as "the nation's oldest major white supremacist prison gang and a national crime syndicate" while the Anti-Defamation League calls it the "oldest and most notorious racist prison gang in the United States". According to the Federal Bureau of Investigation (FBI), the Aryan Brotherhood makes up an extremely low percentage of the entire US prison population, but it is responsible for a disproportionately large number of prison murders.

The gang has focused on the economic activities which organized crime entities typically engage in, particularly drug trafficking, extortion, inmate prostitution, and murder-for-hire. The organization of its whites-only membership varies from prison to prison but it is generally hierarchical, headed by a twelve-man council which is topped by a three-man commission. The Aryan Brotherhood uses various terms, symbols, and images in order to identify itself, including shamrocks, swastikas, and other symbols. In order to join the Aryan Brotherhood, new members may swear a blood oath or take a pledge; acceptance into the Aryan Brotherhood is aided by a prospect's willingness to kill another inmate.