Joseph ben Ephraim Karo, also spelled Yosef Caro, or Qaro, (Toledo, 1488 – Safed, 1575) was author of the last great codification of Jewish law, the Shulchan Aruch, which is still authoritative for all Jews pertaining to their respective communities. To this end he is often referred to as ha-Mechaber (Hebrew: "The Author") and as Maran (Aramaic: "Our Master").

Karo was born in Toledo, Spain in 1488. In 1492, aged four years old, he was forced to flee Spain with his family and the rest of Spanish Jewry because of Jewish expulsion from the Alhambra Decree and subsequently settled in Portugal. After the expulsion of the Jews from Portugal in 1497, Karo went with his parents to Nikopolis in current day Bulgaria, where he received his first instruction from his father, who was himself an eminent Talmudist. He married, first, Isaac Saba's daughter, and, after her death, the daughter of Hayyim Albalag, both of these men being well-known Talmudists. After the death of his second wife he married the daughter of Zechariah Sechsel (or perhaps Sachsel), a learned and wealthy Talmudist.

Already as a young man, he gained a reputation as a brilliant Torah scholar. He began by writing an explanation on the Rambam's Mishneh Torah. He called his work the Kesef Mishnah. Here he cited and explained Rambam's sources.

Between 1520 and 1522 Karo settled at Adrianople. He later emigrated to Palestine, where he arrived about 1535, having en route spent several years at Salonica (1533) and Constantinople.

Karo published during his lifetime:

• Beth Yosef (בית יוסף), a commentary on Arba'ah Turim, the current work of Jewish law in his days;
• Shulchan Aruch (שולחן ערוך), a condensation of his decisions in Beth Yosef;
• Kesef Mishneh (כסף משנה) (Venice, 1574-5), a commentary of Mishneh Torah by Maimonides;

After his death there appeared:

• Bedek ha-Bayit (בדק הבית) (Salonica, 1605), supplements and corrections to Beth Yosef;
• Kelalei ha-Talmud (כללי התלמוד) (Salonica, 1598), on the methodology of the Talmud;
• Avkath Rochel (אבקת רוכל) (Salonica, 1791), Responsa
• Maggid Meisharim (מגיד מישרים) (Lublin, 1646), and supplements (Venice, 1646)
• Derashot (דרשות) (Salonica, 1799), speeches, in the collection 'Oz Tzaddikim'.

Karo also left a commentary upon the Mishnah, as well as supercommentaries to Rashi's and Nahmanides' commentaries on the Torah, which have, apparently, not been preserved.

See also "יוסף קארו"