Joel ben Samuel Sirkis (Hebrew: רבי יואל בן שמואל סירקיש; born 1561 - March 14, 1640) also known as the Bach (an abbreviation of his magnum opus BAyit CHadash), was a prominent Ashkenazi posek and halakhist, who lived in Central Europe and held rabbinical positions in Belz, Brest-Litovsk and Kraków, and is considered to be one of the greatest Talmudic scholars of Poland.

Many of his students became leading rabbis in Poland, the most famous being his son-in-law, David ben Samuel ha-Levi, as well as Gershon Ashkenazi and Menachem Mendel Krochmal.

In 1631 he wrote his magnum opus, Bayit Ḥadash (lit "new house"), a critical and comprehensive commentary on the Arba'ah Turim of Jacob ben Asher, in which he traced each law to its Talmudic source and followed its subsequent development through successive generations of interpretation.

[1][3][4] The Bach's responsum provides a concise overview of the social and economic conditions of Polish Jewry, as well as the relationship between Jews and non-Jews in early 17th century Poland.

One of his responsa, in particular, was censored by the Christian authorities because the work addresses the case of a Jew who was martyred for allegedly stealing a small statue of Jesus.