Abraham Hirsch ben Jacob Eisenstadt of Byelostok (1812–1868) (Hebrew: אברהם צבי הירש בן יעקב אייזנשטאט) was a Russian rabbi in Ottymia (?), government of Kovno. He began at an early age to write his important work, Pithe Teshubah (פיתחי תשובה), which is the most popular and useful index to the responsa and decisions of later authorities on the subjects treated in the Shulḥan 'Aruk. Eisenstadt's great merit consists in having collected all the material given in the works of his predecessors, and in having added to it an almost complete collection of references to responsa of all the later eminent rabbis.