Rabbi Shmiel Dovid Halberstam (Hebrew: שמואל דוד הלברשטאם), also known as the Sanz-Klausenberger Rebbe, is the younger son and one of the successors of Rabbi Yekusiel Yehudah Halberstam, the previous Klausenberger Rebbe. He resides in Brooklyn, New York.

He is one of seven children born in his father's second marriage to Chaya Nechama Ungar, daughter of the Nitra Rav, Rabbi Shmuel Dovid Ungar.^[1] He was named after his mother's father, who was murdered in the Holocaust. His older brother, Rabbi Zvi Elimelech Halberstam, is the Sanzer Rebbe of Israel, and he also has five sisters. He married Tzipora Weider, daughter of Rabbi Aharon Wieder, the Linzer Rav, who was a long-time dayan in the Klausenberger beis din (rabbinical court) in America.^[2]

Rabbi Halberstam is the leader of North American operations for the Mifal HaShas Torah study network founded by his father, and honoree president of the Kolel Chibas Yerushalayim charity organization in the name of Reb Meir Baal HaNess.

He is known for his effusive and lengthy prayers.

• Klausenberg (Hasidic dynasty)
• Sanz (Hasidic dynasty)