Sefer ha-Kuzari following the Venice 1547 edition with a Latin translation by Johan Buxtorf. R. Judah Halevi worked on the Kuzari for 20 years, completing its final draft shortly before his departure for Erez Israel. Although Halevi, in one of his letters, states that he was prompted to write this work by having to answer certain questions posed by a Karaite, it deals only marginally with Karaism. It is a polemical work, directed primarily against Aristotelian philosophy - which Halevi, while being one of the first to recognize the threat it posed to the Jewish faith, greatly respected - and secondarily against Christianity and Islam. While the Kuzari is an apologia rather than a systematic philosophic treatise, it is based upon an original, crystallized, and unified conception of Judaism, developed by Halevi in the course of a thoroughgoing confrontation with philosophy.

The work is called the Kuzari after the king of the Khazars whose conversion to Judaism provides the literary framework of the work. After being told by an angel in a dream that, while his intentions were acceptable to G-d, his actions were not, the king, in an effort to discover how he should lead his life, invites first an Aristotelian philosopher, and then representatives of Islam, Christianity, and Judaism, to discuss with him their respective beliefs. This literary framework enables Halevi to compare the teachings of Judaism with those of Aristotelianism, Islam, and Christianity, in an effort to prove the superiority of Judaism. The work is divided into five parts. In the first part the philosopher, the Christian, and the Muslim expound their views. The king is with the philosopher, and when he realizes that Christianity and Islam are both based on Judaism, he calls in a Jewish scholar. The following four parts are devoted mainly to the dialogue between the king and the Jew. In the second part the king questions the Jewish scholar concerning the attributes of G-d. The scholar, however, is more concerned with the experience of G-d gained through prophecy than with the theoretical knowledge of G-d. Thus, he directs the discussion to the circumstances in which prophecy arose, and to the particular qualities of the people of Israel; of Erez Israel, the Temple, and the Hebrew language. The third part deals with the details of the worship of G-d in Judaism. The scholar explains that worship in Judaism consists in fulfilling the biblical commandments, which originated in divine revelation, and which cannot be interpreted or applied except by means of the authoritative tradition. This last point leads to a detailed argument against Karaism. In the fourth part the scholar discusses the names of G-d, distinguishing between Elohim and Adonai, the former being a general term denoting the god who is known through philosophical reasoning, the latter, a proper name, denoting the G-d of Israel who is known only through revelation and prophecy. He explains prophecy as the experience of being in the presence of G-d or the Shekhinah, an intermediary being between G-d and man - an experience brought about by the special "inner sense" of the prophet. He goes on to discuss the uniqueness of the people of Israel, in that they alone possess the faculty of prophecy, the "inner sense" which enables them to approach the divine presence. Halevi, in order to show that all science originated with the Jews, and that the Jewish people from its inception did not lack any human perfection, concludes this chapter with a summary of, and commentary on, Sefer ha-Yezirah ("The Book of Creation"), which he regarded as a major scientific work, and which he attributed, as did others at the time, to Abraham the Patriarch. In the fifth and final part of the book he takes up the polemic with the philosopher whom he did not properly challenge in the first part. The Jewish scholar, in an ironic vein, presents his pupil with a sketch of the Aristotelian philosophy of his day, at the same time exposing its weaknesses. While Halevi seems better acquainted with the doctrines of Aristotelianism than were his predecessors, it would be wrong to assume that he studied Aristotle's works directly. Halevi's criticism of Aristotelianism is highly reminiscent of al-Ghazali's criticism of philosophy in the Incoherence of the Philosophers (Tahafut al-Falasifa). Halevi also presents his pupil with an outline of the arguments of the kalam, of which he does not approve any more than he does of Aristotelianism. Though he considers these arguments useful for polemics, he believes they have no great intrinsic value.

First printed in Fano in 1506, it has been reissued many times. The Kuzari was translated into English (H. Hirschfeld, 1905; reprinted with an introduction by H. Slonimsky, 1964; abridged version with introduction by I. Heinemann, 1947), Latin, Spanish, German, French, and Italian.