Aleinu (Hebrew: עָלֵינוּ, "it is our duty") or Aleinu leshabei'ach ("[it is] our duty to praise [ God ]"), meaning "it is upon us or it is our obligation or duty to praise God," is a Jewish prayer found in the siddur, the classical Jewish prayerbook. It is recited at the end of each of the three daily Jewish services. It is also recited following the New Moon blessing and after a circumcision is performed. It is second only to the Kaddish (counting all its forms) as the most frequently recited prayer in current synagogue liturgy.

A folkloric tradition attributes this prayer to the biblical Joshua at the time of his conquest of Jericho. This might have been inspired by the fact that the first letters of the first four verses spell, in reverse, Hoshea, which was the childhood name of Joshua (Numbers 13:16). Another attribution is to the Men of the Great Assembly, during the period of the Second Temple. An early - that is, pre-Christian - origin of the prayer is evidenced by its explicit mention of bowing and kneeling - practices associated with the Temple, and its non-mention of exile or a desire to restore Israel or the Temple.