The kazoku (華族, lit. "flowery lineage") was the hereditary peerage of Japan that existed between 1869 and 1947.

The Meiji oligarchs, as part of their Westernizing reforms, merged the kuge (the court nobility in Kyoto) and the daimyo (or feudal lords) into a single aristocratic class in 1869. Ito Hirobumi, one of the leaders of the Meiji Restoration and later the principal author of the 1889 Constitution of the Empire of Japan, intended the kazoku to serve a political and social bulwark for the "restored" emperor and the Japanese imperial institution.

In addition to the existing Japanese nobility, the Meiji leadership also awarded kazoku status to those regarded as having performed outstanding service to the country. In 1884, the government took the further step of dividing the kazoku into five ranks explicitly based on the British peerage:

1. prince or duke (公爵 kōshaku)
2. marquis (侯爵 kōshaku)
3. count (伯爵 hakushaku)
4. viscount (子爵 shishaku)
5. baron (男爵 danshaku)

As in British peerage, only the actual holder of a title and his consort were considered part of the kazoku. The holders of the top two ranks, prince and marquis, automatically became members of the House of Peers upon their succession or upon majority (in the case of peers who were minors). Counts, viscounts, and barons elected up to 150 representatives from their ranks to the House of Peers.

Titles passed according to primogeniture, although kazoku houses frequently adopted sons from collateral branches of their own houses and other kazoku houses to prevent their lines from dying out. A 1904 amendment to the 1889 Imperial Household Law, allowed minor princes (ō) of the imperial family to renounce their imperial status and become peers (in their own right) or heirs to childless peers. Initially there were 11 non-imperial princes or dukes, 24 marquis, 76 counts, 324 viscount, and 74 barons, for a total of 509 peers. By 1928, through promotions and new creations there were a total of 954 peers: 18 non-imperial princes or dukes, 40 marquis, 108 counts, 379 viscounts, and 409 barons.

Rank distribution for kazoku houses of kuge descent depended on the highest possible office to which its ancestors had been entitled in the imperial court. Thus, the heirs of the five regent houses (go-seike) of the Fujiwara dynasty (Konoe, Takatsukasa, Kujo, Ichijo, and Nijo) all became princes. The heads of other kuge houses (including Daigo, Hamuro, Hirohata, Kikutei, Kuga, Kazan'in, Nakamikado, Nakayama, Oimikado, Saga, Saionji, Shijo, and Tokudaiji) became marquises. Also, the head of the Sho family, the former royal family of the Ryukyus (Okinawa), was given the title of marquis.

Excluding the Tokugawa, kazoku rank distribution for the former daimyo depended on rice revenue: those with 150,000 koku or more became marquises, those with 50,000 koku or more become counts, etc. The former shogun, Tokugawa Yoshinobu became a prince, the heads of primary Tokugawa branch houses (shimpan daimyo) became marquises, and the heads of the secondary branches became counts.

The Constitution of Japan abolished the kazoku and ended the use of all titles of nobility or rank, outside the imperial family. Nonetheless, the descendants of former kazoku families continue to occupy prominent roles in Japanese society and industry.