The Sixth Yamaguchi-gumi (六代目山口組 ,Rokudaime Yamaguchi-gumi?) is Japan's largest and most infamous yakuza organization, and is named after founder Harukichi Yamaguchi.

It is one of the largest criminal organizations in the world. Estimates put the number of active members at just over 39,000, with thousands more having strong associations. It is, by far, the largest of the boryokudan groups, and its membership encompasses roughly 45% of the 86,300 yakuza in the Japanese underworld. Formal members of the Yamaguchi-gumi are 102 total people; 1 kumicho, 15 shatei (younger brother) and 86 wakachu (child) as of November 2005.

The Yamaguchi-gumi are among the world's wealthiest gangsters, bringing in billions of dollars a year from extortion, gambling, the sex industry, guns, drugs, and real estate and construction kickback schemes. They are also involved in stock market manipulation and Internet pornography.

The Yamaguchi-gumi has its headquarters in Kobe, Japan, but it operates all across Japan and has overseas operations in Asia and the United States.[citation needed] Despite more than a decade of police crackdowns, their numbers have been growing. Its current kumicho (Don), Shinobu Tsukasa, has declared an expansionist policy - even making inroads into Tokyo, traditionally not Yamaguchi turf.