Shinnōke (literally shinnō houses) were the collective name of four cadet branches of the Imperial Household of Japan, entitled to provide a successor to the Chrysanthemum throne if the main line failed to produce an heir. The heads of these houses generally held the title of shinnō (imperial prince), regardless of their genealogical distance from the reigning tennō (or Emperor). Thus, remote descendants of previous emperors would retain imperial status in perpetuity. Younger sons in these princely houses were titled ō, unless they succeeded to the headship of the house or were specially designated shinnō (and thus a potential successor to the throne) by the emperor. Daughters were titled nyoō.

Just as a remotely related shinnō could succeed to the throne in default of a direct heir, likewise an emperor's biological son, grandson, or a non-heir son from another shinnōke could succeed to sonless shinnōke. Prince Haruhito, the younger brother of Emperor Kōkaku, for example, succeeded to the head of the Kan'in-no-miya. Likewise, the Katsura-no-miya house faced extinction several times, each time to be resurrected by an Emperor placing a son in the house. Finally, when the five-generation Kan'in-no-miya house faced extinction in 1872, Emperor Meiji directed Prince Kotohito, the sixteenth son of Fushimi no miya Kuniye and an adopted son of Emperor Kōmei, to succeed to that title.

Before the Meiji Restoration, non-heir sons in both the main imperial house (that is, the emperor's sons and grandsons) and the shinnōke had two career options. A non-heir son could "descend" to subject status with a noble surname such as Minamoto or Taira. Alternatively, a non-heir son could enter the Buddhist priesthood, generally as the head of one of the monzeki temples in and around Kyoto. During the Tokugawa shogunate (1605-1867), the latter practice became almost universal. Non-heir sons who entered the priesthood were styled hoshinnō or hoō. These princely priests were automatically excluded from the succession, but could be recalled to "secular" status (and thus reinstated as potential successors, in the case of hoshinnō). Daughters were frequently used as pawns to cement matrimonial alliances with kuge and daimyō houses. Unwed daughters often became Buddhist nuns.

There were four shinnōke in the Edo period. They were, in order of creation:

1. Fushimi-no-miya
2. Katsura-no-miya
3. Arisugawa-no-miya
4. Kan'in-no-miya.

Emperor Kōkaku, the lineal ancestor of all subsequent emperors, was a scion of the Kan'in-no-miya. The Katsura-no-miya and Arisugawa-no-miya houses died out in 1881 and 1913, respectively. The sixteenth son of Prince Kuniye, the twentieth head of the Fushimi no miya, succeeded to the Kan'in no miya house in 1875. The Fushimi-no-miya house was the progenitor of nine other cadet branches of the imperial family, the ōke, during the reign of Emperor Meiji. The Fushimi no miya and its offshoots were reduced to commoner status as part of the American occupation reforms in October 1947.