Av Beis Din

The av beit din (Hebrew: אָב בֵּית דִּין‎ ʾabh bêth dîn, "chief of the court"), also spelled av beis din or abh beth din and abbreviated ABD (אב״ד‎), 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.

The Av Beit Din presided over the Sanhedrin in the absence of the Nasi, and was the chief of the Sanhedrin when it sat as a criminal court. He sat with seven other judges while hearing a case.

The last Av Beth Din in Jewish tradition is Menahem the Essene who abdicated to "serve the King" in 20CE. Caiaphas was set to be next Av Beth Din but was opposed by the House of Shammai until Gamaliel became Nasi. Talmudic Judaism does not recognise any Av Beth Din after Menachem.

In modern times it is used as an honorific title for the presiding rabbi of a beth din (rabbinical court), who is typically the salaried rabbi of the local Jewish community and usually a posek ("decisor" of Halakha). It is also abbreviated as AB"D when it is after the name of the Chief Rabbi of a national Jewish community.

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