Av Beit Din, Av Beis Din, or Abh Beth Din (abbreviated: AB"D) (Hebrew: אב בית דין‎‎, "Chief of the Court") was the second-highest-ranking member of the Sanhedrin during the Second Temple period. The president, who bore the title Nasi "Prince", was in a way the supervisor, but not a member of the court, which consisted of seventy members. The most learned and important of these seventy members was called Av Beit Din, a title similar to that of vice-president.