Aryan Brotherhood (AB) originated in San Quentin prison in 1967. Originally, this gang was established to provide protection for white individuals from black and Hispanic groups, most specifically the Mexican Mafia. Some of the original members of the AB migrated from a 1950s gang known as the "Bluebirds." Other names used in the past were the "Diamond Tooth Gang" and the "Nazi Gang." Today, they number about 15,000 members in and out of prison. In March 2006, four AB leaders were indicted for numerous crimes, including murder, conspiracy, drug trafficking, and racketeering. According to the FBI, although the gang makes up less than one percent of the prison population, it is responsible for up to 26% of murders in the federal prison system. Although members of the AB ordinarily wear numerous tattoos, the true AB tattoo is a shamrock, the letters AB, and three sixes. Three sixes displayed alone are not AB-specific because they are used by several other gangs. Only members of the AB are permitted to wear the "brand" of the gang; individuals found to be wearing the tattoo without consent of the AB are subject to murder. The AB has discouraged newer members from displaying AB specific tattoos to avoid identification from law enforcement officials. As a result, some AB members have removed or disguised their tattoos. Although the Brotherhood is a white supremacist organization, for most AB members crime is their number one priority, with racial hatred being a secondary goal. The true white supremacist’s number one goal is generally racial hatred, which they may or may not achieve through criminal behavior. Since 1972, the Aryan Brotherhood has had an alliance with the Mexican Mafia. It has also used the Odinist religion to conduct gang meetings and disguise illicit business practices. Older AB members learned the American Sign Language to communicate covertly. The AB has spread throughout the nation and in the federal prison system.

Its leadership was recently hit with a federal R.I.C.O. indictment. Although the leadership has been disrupted, law enforcement officials expect the gang to maintain a low profile and continue to contract out their criminal activity to such groups as the Nazi Low riders and Peni (Public Enemy Number One). The AB is separated into two main groups, one in the federal prison system, the other consisting of numerous factions of the Brotherhood in various state prison systems, notably California, which is loosely affiliated to a greater or lesser degree. Each faction is controlled by a three-man commission, which controls and supervises gang activities. These gangs in the state system, splinter groups or copycats, are usually tolerated by members of the federal prison or California factions, but intra-gang violence is not uncommon. Organization at lower levels varies from prison to prison. For example, in the Arizona prison system, members are known as "kindred" and organize into "families". A "council" controls the families. Kindred may recruit other members, known as "progeny", and serve as a mentor for the new recruit.
Membership generally (though not exclusively) consists of white male prisoners and operates on a "blood in, blood out" system. That is, a candidate for membership must assault and kill another prisoner to enter the gang. Membership is for life, and those attempting to leave may likewise be assaulted or killed by other members. Both federal and state members swear the same oath:
An Aryan brother is without a care/He walks where the weak and heartless won't dare/For an Aryan brother, death holds no fear/Vengeance will be his, through his brothers still here.”
The AB has since focused on the economic activities typical of organized crime entities, particularly drug trafficking, extortion, prostitution, and murder-for-hire. According to a recent federal indictment, the Brotherhood has partnered with Asian gangs to import heroin from Thailand.While incarcerated in Marion Federal Penitentiary in 1996, after being assaulted, Gambino crime family boss John Gotti is known to have asked Aryan Brotherhood members to murder his attacker, although the hit was unsuccessful. The overwhelming majority of Aryan Brotherhood members were originally sent to prison for crimes not motivated by racial bigotry, such as robbery, drug dealing, and assault, and join the Aryan Brotherhood out of a need for protection or camaraderie. However, members are expected to continue AB activities after being released, and are known to commit hate crimes after joining the gang.
Until the 1960s, most prisons in the United States were racially segregated. As prisons began to desegregate, inmates organized along racial lines. Prosecutors of cases against the gang say it was formed in reaction to getting raped by other races in prison. The AB may have been derived from or inspired by a previous entity, the Bluebird Gang. In the early 1970s, the Aryan Brotherhood began working closely with the Mexican Mafia and began focusing on drug trafficking and other economic activities.In 1973, the California branch of the Aryan Brotherhood rejected Charles Manson when he asked them for protection against black inmates, because he had murdered a pregnant woman. The AB considered this dishonorable and turned him down initially. However, it eventually realized that Manson's followers could be exploited, so it began protecting Manson while his followers smuggled drugs and weapons into prisons. By 1980, the gang had split into two distinct factions, one within the federal prison system and one outside of state prison systems. In 1982, an anonymous source gave information to the FBI implicating the AB in two high profile murders in the California state prison system. Released or paroled members have smuggled money or drugs into prison, including marijuana, cocaine, and methamphetamines. The creed by which the Brotherhood members operate under is:
"I will stand by my brother My brother will come before all others My life is forfeited should I fail my brother I will honor my brother in peace and war"
They also live by the motto, "In for life and out by death."