The Bar Kokhba revolt (Hebrew: מֶרֶד בַּר כּוֹכְבָא‎, Mereḏ Bar Kōḵḇāʾ‎), also known as the Third Jewish Revolt or the 'Jewish Expedition' as the Romans named it (Latin: Expeditio Judaica), was a rebellion by the Jews of the Roman province of Judea, led by Simon bar Kokhba, against the Roman Empire. The last of the three Jewish-Roman Wars, it was fought c. 132–136 CE.

The revolt erupted as a result of religious and political tensions in Judea following on the failed First Revolt in 66–73 CE, including the establishment of a large Roman military presence in the province, changes in administrative and economic life, and the failure of revolts in the diaspora. The immediate reasons seem to be the construction of a new city, Aelia Capitolina, over the ruins of Jerusalem and the erection of a temple to Jupiter on the Temple Mount. The Church Fathers and rabbinic literature emphasize the role of Rufus, governor of Judea, in provoking the revolt. The charismatic and messianic nature of Bar Kokhba himself may have also been a factor.

In 132, the revolt quickly spread across Judea. Despite the arrival of Roman reinforcements, initial rebel victories established an independent state, the "House of Israel", over much of the province for over three years. Bar Kokhba took the title of Nasi ("head of state"), and many Jews regarded him as the Messiah, who would restore their national independence. This setback, however, led Hadrian to assemble a large army from across the Empire, which invaded Judea in 134 under the command of Julius Severus. It was made up of six full legions with auxiliaries and elements from up to six additional legions, which finally crushed the revolt.

The Bar Kokhba revolt had disastrous effects on the Jewish population of Judea, even more so than during the First Jewish–Roman War, to an extent that some scholars describe as a genocide. Based on the ancient sources and archeological evidence, Judea was depopulated as a result of many Jews being killed or expelled, and a significant number of captives were sold into slavery. Jews were subjected to a series of religious edicts. Roman casualties were also considered heavy – XXII Deiotariana was disbanded, perhaps due to serious losses. Whether Jews became a minority in the Land of Israel after the revolt is uncertain, but it is evident that Jews continued to live in the Galilee, Golan, Bet Shean Valley, and the periphery of Judea.

The Bar Kokhba revolt greatly influenced the course of Jewish history, philosophy and religion. Despite easing the persecution of Jews following Hadrian's death in 138 CE, the Romans barred Jews from Jerusalem, except for attendance in Tisha B'Av. Jewish messianism was abstracted and spiritualized, and rabbinical political thought became deeply cautious and conservative. The Talmud refers to Bar Kokhba as "Ben-Kusiba", a derogatory term meaning "son of deception", indicating that he was a false Messiah. It was also among the key events to differentiate Christianity as a religion distinct from Judaism.