Piskei HaSiddur is an early 19th-century work of halakhic rulings relating to prayer by Rabbi Shneur Zalman of Liadi, founder of the Chabad (Lubavitch) branch of Chasidic Judaism. Piskei HaSiddur is often printed as part of Siddur HaRav, a prayer book edited by Shneur Zalman based on Rabbi Isaac Luria’s prayer book. The rulings in Piskei HaSiddur occasionally contradict parallel rulings in Shneur Zalman’s legal code, Shulchan Arukh HaRav. In those cases, Chabad Chasidim generally follow the rulings of Piskei HaSiddur, which was compiled later.