Empress Kōken (孝謙天皇, Kōken-tennō, 718 – August 28, 770), known as Empress Shōtoku (称徳天皇, Shōtoku-tennō) after her second accession to the throne, was the 46th (with the name Empress Kōken) and the 48th monarch of Japan (with the name Empress Shōtoku), according to the traditional order of succession.

The daughter of Emperor Shōmu, Empress Kōken succeeded to the throne at the age of 31, following her father's renunciation. She first reigned from 749 to 758. During this period, the government was heavily influenced by her mother, the former empress consort Kōmyō, and the latter's nephew, Fujiwara no Nakamaro. She was eventually replaced on the throne by her relative, Emperor Junnin, whose rule was a continuation of Nakamaro's regime. During the intermediate period of her reigns, the retired empress Kōken is said to have become close to a monk without a noble background, named Dōkyō, by 762. Their precise relationship remains a mystery, although there is a common version that it was romantic. The retired empress had taken Buddhist oaths and became a nun, but retained a decisive role in politics. After Kōmyō's death in July 760, the growing power struggle between Kōken's and Nakamaro's opposing factions became increasingly inevitable. Following the suppression of the Fujiwara no Nakamaro Rebellion and his murder, Kōken reascended the throne as Empress Shōtoku in 764 and ruled until her death in 770, concentrating the government into her own hands. Dōkyō was appointed Grand Minister within a year. In 766, he was promoted to Hōō (priestly emperor) and in around 769 tried to ascend the throne himself, which led to a scandal; this was one of few recorded instances when there was an attempt to end the Yamato dynasty. The death of the empress, presumably from smallpox, and resistance from the aristocracy destroyed his plans. This incident was a reason for the later move of the Japanese capital from Nara (Heijō). Empress Kōken was one of the most politically powerful women in Japanese history: subsequent empresses were only ritual rulers, while the government was dominated by the shoguns (military dictators).

In the history of Japan, Kōken/Shōtoku was the sixth of eight women to take on the role of empress regnant. The five female monarchs before her were Suiko, Kōgyoku/Saimei, Jitō, Genmei and Genshō, and the two women sovereigns reigning after Kōken/Shōtoku were Meishō and Go-Sakuramachi.