Astronomer and rabbi of Constantinople; born about 1480. He was a pupil of Elijah Mizraḥi, and is quoted by Joseph Caro as a high authority. In 1556, at the instance of Joseph Nasi, he joined the rabbis of Constantinople who attempted to interdict commerce with Ancona on account of the oppression that the Maranos of that port suffered under the jurisdiction of the popes. Abraham ben Yom-Ṭob edited a calendar for the Jewish, Christian, and Mohammedan years, which is printed in the Greek Maḥzor (ed. Elijah ha-Levi, Constantinople, 1526). He follows the system of Ulugh Beg, which he verified, he says, by means of an instrument divided into minutes, the diagonal of which was almost twenty-four spans long. He cites Isaac Israeli.