Chaim Ozer Grodzinski (Hebrew: חיים עוזר גראדזענסקי‎; August 24, 1863 – August 9, 1940) was a pre-eminent Av beis din (rabbinical chief justice), posek (halakhic authority), and Talmudic scholar in Vilnius, Lithuania in the late 19th and early 20th centuries. During his 55 years of community service, he was recognized as the leading posek and spiritual guide of his generation, fielding halakhic queries from all parts of the world and being consulted on every Jewish communal issue. He played an instrumental role in preserving Lithuanian yeshivas during the Communist era, and saved the yeshivas of Poland and Russia during the Nazi invasion of Poland in 1939, when he arranged for these yeshivas to relocate to Lithuanian cities.