Avinu Malkeinu (Hebrew: אָבִינוּ מַלְכֵּנוּ; "Our Father, Our King") is a Jewish prayer recited during Jewish services on Rosh Hashanah and Yom Kippur, as well on the Ten Days of Repentance from Rosh Hashanah through Yom Kippur. In the Ashkenazic tradition, it is recited on all fast days; in the Sephardic tradition only because it is recited for the Ten Days of Repentance does it occur on the fast days of Yom Kippur and the Fast of Gedaliah.
Joseph H. Hertz (died 1946), chief rabbi of the British Empire, described it as "the oldest and most moving of all the litanies of the Jewish Year." It makes use of two sobriquets for God that appear separately in the Bible; "Our Father" (Isaiah 63:16) and "Our King" (Isaiah 33:22).
The Talmud (T.B. Ta'anith 25b) records Rabbi Akiva (died 135 CE) reciting two verses each beginning "Our Father, Our King" in a prayer to end a drought (apparently successfully). In a much later compilation of Talmudic notes, published circa 1515, this is expanded to five verses. It is very probable that, at first, there was no set number of verses, no sequence, nor perhaps any fixed text. Apparently an early version had the verses in alphabetic sequence, which would mean 22 verses. The prayer book of Amram Gaon (9th century) had 25 verses. The Mahzor Vitry (early 12th century) has more than 40 verses and added the explanation that the prayer accumulated additional verses that were added ad hoc on various occasions and thereafter retained. Presently, the Sephardic (Spanish and Portuguese) tradition has 29 verses, among the Mizrahi Jews the Syrian tradition has 31 or 32 verses, but the Yemenite has only 27 verses, the Salonika as many as 53 verses, the Ashkenazic has 38 verses, the Polish tradition has 44 verses, all with different sequences. And within traditions, some verses change depending on the occasion, such as Rosh Hashana (when it is said kotvenu - "inscribe us"), or the Ne'ila Yom Kippur service (chotmenu - "seal us"), or a lesser fast day (zokhrenu - "remember us").