Mito (水戸藩, Mito-han) was a Japanese domain of the Edo period. It was associated with Hitachi Province in modern-day Ibaraki Prefecture.

In the han system, Mito was a political and economic abstraction based on periodic cadastral surveys and projected agricultural yields. In other words, the domain was defined in terms of kokudaka, not land area. This was different from the feudalism of the West.

The domain's capital was the city of Mito. Beginning with the appointment of Tokugawa Yorifusa by his father, Shōgun Tokugawa Ieyasu, in 1608, the Mito branch of the Tokugawa clan controlled the domain until the abolition of the han system in 1871. During the Edo period, Mito represented the center of nativism largely as a result of the Mitogaku, an influential school of Japanese thought, which advanced the political philosophy of sonnō jōi ("revere the emperor, expel the barbarians") that had become a popular sentiment after 1854. Mito's sponsorship of the Dai Nihon-shi (A History of Great Japan) established the domain's tradition of intellectualism. Later, Mito scholars and their ideology influenced many of the revolutionaries involved in the Meiji Restoration.

Following the establishment of the Tokugawa shogunate in 1603, Tokugawa Ieyasu appointed his eleventh son, Tokugawa Yorifusa, as daimyō in 1608. With his appointment, Yorifusa became the founding member of the Mito branch of the Tokugawa clan. Along with the Tokugawa branches in Kii and Owari, the Mito branch represented one of three Tokugawa houses known as the gosanke.

Although the Mito branch held less land and wealth than either of the other two branches, they maintained considerable influence throughout the Edo period. The domain's promiximity to the de facto capital in Edo was a contributing factor to this power as well as the fact that many people unofficially considered the Mito daimyō to be "vice-shōgun".

Nakayama Nobuyoshi (ja), a young samurai whose father's sacrifice at Odawara was recognized by Ieyasu, was taken in by Ieyasu as a page. Following Sekigahara, he would be rewarded for his service by being named chief retainer to Yorifusa, and his descendants subsequently given the hereditary lordship of the Matsuoka Domain as a subordinate domain of Mito following his own bravery serving Yorifusa at Osaka.

Tokugawa Mitsukuni, the third son of Tokugawa Yorifusa, became the second daimyō of Mito in 1661. Mitsukuni further established Mito's status as a respected han by sponsoring the Dai Nihon-shi in 1657. The endeavor would launch Mito's reputation as a center for intellectual thought.

The Mito School (Mitogaku) was an influential school of Japanese thought which advocated isolationism, nativism, and reverence of the emperor. The origins of this Neo-Confucianist movement date to Mitsukuni's decision to establish a historiographical organization known as the Shōkōkan in 1657. Mitsukuni recruited educated scholars to the Shōkōkan to study the history and philosophy of Japan. Mitsukuni initiated the creation of the Dai Nihon-shi by the scholars in order to compile a history of Japan which would focus on the imperial line. Each chapter of the "Annals" in the Dai Nihon-shi concentrated on the rule of a specific emperor. The project took more than two hundred and fifty years to finish, and it was officially published in 1906.