The Sanhedrin (Hebrew and Aramaic: סַנְהֶדְרִין; Greek: Συνέδριον, synedrion, 'sitting together,' hence 'assembly' or 'council') was an assembly of either 23 or 71 elders (known as "rabbis" after the destruction of the Second Temple), appointed to sit as a tribunal in every city in the ancient Land of Israel.

There were two classes of Rabbinite Jewish courts which were called Sanhedrin, the Great Sanhedrin and the Lesser Sanhedrin. A lesser Sanhedrin of 23 judges was appointed to sit as a tribunal in each city, but there was only supposed to be one Great Sanhedrin of 71 judges, which among other roles acted as the Supreme Court, taking appeals from cases which were decided by lesser courts. In general usage, the Sanhedrin without qualifier normally refers to the Great Sanhedrin, which was presided over by the Nasi, who functioned as its head or representing president, and was a member of the court; the Av Beit Din or the chief of the court, who was second to the nasi; and 69 general members.

In the Second Temple period, the Great Sanhedrin met in the Temple in Jerusalem, in a building called the Hall of Hewn Stones. The Great Sanhedrin convened every day except festivals and the sabbath day (Shabbat).

After the destruction of the Second Temple and the failure of the Bar Kokhba revolt, the Great Sanhedrin moved to Galilee, which became part of the Roman province of Syria Palaestina. In this period the Sanhedrin was sometimes referred as the Galilean Patriarchate or Patriarchate of Palaestina, being the governing legal body of Galilean Jewry. In the late 200s CE, to avoid persecution, the name Sanhedrin was dropped and its decisions were issued under the name of Beit HaMidrash (house of learning). The last universally binding decision of the Great Sanhedrin appeared in 358 CE, when the Hebrew calendar was established. The Great Sanhedrin was finally disbanded in 425 CE after continued persecution by the Eastern Roman Empire.

Over the centuries, there have been attempts to revive the institution, such as the Grand Sanhedrin convened by Napoleon Bonaparte, and modern attempts in Israel.