R. Isaac's monumental work Or Zaru'a shared the fate of similar halakhic works which were apparently not sufficiently copied because of their extensive nature, and as a result did not achieve large circulation. Only 600 years after his death were the first two parts of the work published (1862) from a manuscript in the possession of Akiva Lehren of Amsterdam. The first part deals with blessings, laws connected with the land of Israel, niddah and mikva'ot, laws of marriage, and a collection of responsa, mostly by the author, but some by other scholars. Part II contains topics which are now included in the Orah Hayyim section of the Shulhan Arukh. Two further parts were published at a later date (1887–90) from a manuscript in the British Museum. These contain halakhic rulings derived from the tractates Bava Kamma, Bava Mezia, Bava Batra, Sanhedrin, and Avodah Zarah. A supplement to this section, comprising decisions based on the tractate Shevu'ot, which had not been published in the previous collections because they were thought to pertain to tractate Shevi'it, was published by A. Freimann (in Festschrift zu I. Lewy... (1911), Heb. pt. 10–32). A number of abridgments have been made of the work, the best known of which is that by R. Isaac's son R. Hayyim b. Isaac Or Zaru'a, entitled Simanei Or Zaru'a which achieved a wide circulation although this work too was not at the disposal of all scholars. The quotations from R. Isaac Or Zaru'a in the Haggahot Asheri of R. Israel of Krems are from this abridgment. Although the work did not have a wide circulation, later authorities quote his views to a considerable extent from secondary sources, such as the Mordecai, the Haggahot Maimuniyyot, etc. The complete work constitutes a valuable collection of the halakhic rulings of German and French scholars, as well as being of great value for the history of Jewish communities in Europe during the Middle Ages (for instance, he discusses whether "our brothers in Bohemia" are permitted to carry arms on the Sabbath when they have to guard the city). A great part of the work is derived from his teacher R. Eliezer b. Joel ha-Levi, whose Ravyah was already available to R. Isaac. There is no definite information as to how the work was composed and edited, or the order in which the various parts were written. Before compiling the book, the author made notes and assembled data which were later written up, as he himself states (Or Zaru'a, pt. II, no. 38). He was still engaged in its compilation in 1246 (idem, Av. Zar. no. 107).

חלק א: על סדר זרעים, נשים, קדשים וטהרות. [2], 232 עמ'. עמ' 12-5: "אלפא ביתא". "מלאני לבבי אני... המחבר... לפלפל באותיות של אלפא ביתא... לדרוש אלף האותיות שלו...". עמ' 232-205: שאלות ותשובות. חלק ב: על סדר מועד. 4, 184 עמ'.