Yosef Shalom Elyashiv was a Haredi rabbi and posek who lived in Jerusalem. Until his death at the age of 102, Rav Elyashiv was the paramount leader of both Israel and the Diaspora Lithuanian-Haredi community, and many Ashkenazi Jews regarded him as the posek ha-dor, the contemporary leading authority on halakha, or Jewish law.

In Jewish law, a posek is a legal scholar who determines the application of halakha, the Jewish religious laws derived from the written and Oral Torah in cases of Jewish law where previous authorities are inconclusive, or in those situations where no clear halakhic precedent exists.