The Book of Comparison between the Hebrew and Arabic Languages (Kitab al-Muwazanah) is the monumental work of Rabbi Yitzhak ben Baron, in which he summarized the achievements of comparative Semitic linguistic scholars in the 10th–11th centuries. Ben Baron, a Renaissance man, was close in Spain at the turn of the 11th–12th centuries to the spiritual giants Rabbi Moshe ibn Ezra and Rabbi Yehuda Halevi, offers a systematic, in-depth, and innovative analysis of the structural and lexical relationship between Hebrew and Arabic, based on the teachings of Rabbi Yonah ibn Jannah and the traditions of classical Arabic grammar and lexicography. This edition presents for the first time all the remains of the work that have been discovered to date, edited in a critical, translated, and annotated edition, accompanied by a detailed introduction and a profound and extensive "Elucidations" section that sheds new light on Ben Baron's teachings.