Beit Yosef is a comprehensive commentary on the Arba'ah Turim, citing and analyzing the Talmudic, Geonic, and major subsequent halachic authorities.
Thirty-two authorities, beginning with the Talmud and ending with the works of Rabbi Israel Isserlein (1390–1460 and known as the Terumath ha-Deshen), are summarized and critically discussed in Beit Yosef.
Karo evidences not only an astonishing range of reading, covering almost the entire rabbinic literature up to his time, but also remarkable powers of critical investigation.
The proliferation of printed books, moreover, dramatically increased the availability of halakhic literature; so that many half-educated persons, finding themselves in possession of legal treatises, felt justified in following any ancient authority at will.
Karo undertook his Beit Yosef to remedy this problem, quoting and critically examining in his book the opinions of all the major authorities then known.