(Hebrew: בית יוסף / Spelling: Beit Yosef, Beth Yosef.)
A commentary on the Tur written by Rabbi Yosef Karo, it is a compilation of many emitted sources and the Halachic opinions of early Poskim.
Rabbi Yosef Caro started working on the Bais Yosef while living in Adrianople, when he was around 30 years old. When Rabbi Yosef Karo reached Tzfat he worked with his teacher Rabbi Ya’akov Beirav to complete the book. In all, the Beit Yosef took 20 years to write and another 12 to edit and format. It was created at a very needed time, when different Jewish communities were being uprooted and new communities were forming and had no central Halachic work to guide them. Work done for the Beit Yosef served as the foundation for the eventual creation of the Shulchan Aruch.
In the Bais Yosef, Rabbi Yosef Karo gathered all Halachic rulings from recent and older Poskim as well as their sources in the Talmud, Midrashim and Geonim and applied them to their setting in the Tur. Originally Rabbi Yosef Caro intended the Beit Yosef to be a book in itself but ended up creating it as an appendix to the Tur. There was even a point where he considered structuring it on the Yad Hachazaka but disregarded the idea since the Rambam did not include any sources at all, which would result in a very bulky and extended text. The Bais Yosef also fixes a number of printing errors that fell into the text of the Tur over the years.
Sections of the Beit Yosef were initially published separately; Orach Chaim (Venice 1550), Yoreh Deah (Venice 1551), Even Haezer (Sabbionetta 1553), Choshen Mishpat (Sabbionetta 1559). Due to great demand, the entire Bais Yosef was reprinted shortly afterwords (Venice 1564).
With its publication, the Bais Yosef met opposition from a number of leading Rabbis. They were concerned that it would lead to a laxity amongst Torah scholars who would no longer have to research the roots of each Halacha in the Talmud.
 Rabbi Yosef ibn Lev
One of the main opponents of the Bais Yosef was Rebbe Yosef ibn Lev head of the Salonica Yeshiva who forbade its use amongst his students. Rebbe Yosef ben Lev would give a daily Shiur on the Tur in front of sixty students, each a master in one Masechta of the Talmud. After reciting each Halacha he would call upon the student whose Masecta the law was rooted in, asking him to recite the sources for all to hear. If the student could not do so, Rebbe Yosef ibn Lev would himself trace the Halachic sources via memory, never making a mistake. One day neither he nor any of the students could recall the source of a Halacha and were unable to remember it under any circumstances. Finally Rebbe Yosef ben Lev asked for a copy of the Beit Yosef where he easily located the source of the Halacha. He took this indecent as a divine sign that the books of Rabbi Yosef Caro were destined to be studied by all due to the weakness of newer generations. Rabbi Yosef ibn Lev then instructed his students to start using the Bais Yosef.