"Boryokudan" literally means "violence group," and the Anti-Boryokudan law enacted in 1991 defines "Boryokudan" as "any organization that is likely to help its members to collectively and habitually commit illegal acts of violence." A review of the history of Boryokudan traces its origin to the gamblers and street vendors after World War II. The implementation of the Anti-Boryokudan law in 1992 has resulted in the dissolution of 192 Boryokudan organizations and a reduction in the influence of remaining groups; however, their loan-sharking activities and other income-producing criminal activities remain significant. This paper provides information on Boryokudan rivalry conflicts and firearms-related crimes, as well as strategies for enforcing Anti-Boryokudan law. This includes efforts to expel Boryokudan from involvement in and the exploitation of legitimate businesses. The paper's section on Aum Shinrikyo, a religious group, notes that its members murdered a lawyer in 1989 and killed 18 people with sarin gas attacks in the mid-1990's. The investigation of and the protection of citizens from the Aum Shinrikyo are briefly described. Foreign-based criminal syndicates active in Japan in recent years are also described, along with their criminal activities in Japan.