Aryeh Tzvi Frumer (; also spelled "Fromer" or "Frommer"; 18842 May 1943) was a leading Orthodox rabbi, rosh yeshiva, and posek (halachic authority) in 20th-century Poland. Known as the Kozhiglover Rav after his short term as Rav of Koziegłowy, he served as rosh yeshiva of the yeshiva in Sochaczew (Sochatchov) from 1910 to 1914 and rosh yeshiva of Yeshivas Chachmei Lublin, the premier yeshiva of Poland, from 1934 to 1939. During the German Occupation of Poland, he was incarcerated in the Warsaw Ghetto. In spring 1943 he was deported to the Majdanek concentration camp, where he was murdered. His book of responsa, "Eretz Tzvi" (The Fairest Land) is widely quoted to this day.