Kilayim is the prohibition of mixed species. The Torah (Lev. 19:19; Deut. 22:9–11) lists a number of different examples of mixtures that are prohibited as mixed species. The halakhah reflected in the Mishnah and related works classifies the prohibitions under at least five categories: (1) interbreeding of animals (Ch. 8); (2) planting mixed seeds (Chs. 2 and 3), understood to include the grafting of trees (1:4, 7–8); (3) sha'atnez: mixing wool and linen in garments (Ch. 9); (4) planting grain or greens in a vineyard (Chs. 4–7); (5) ploughing or doing other work with two different species of animal (8:2–4). In its ten chapters, the Mishnah Kilayim deals with the regulations governing all five. In contrast to the assumption of the rabbinic halakhah, mixed seeds was not accepted as a separate biblical prohibition by some early traditions, who applied the relevant scriptural expression to the prohibition of grain in a vineyard. Although the kil'a'im laws themselves were derived from a relatively straightforward reading of the Torah, the details discussed in the tractate were deduced through the exercise of logic, analogies with other areas of law, or by application of the general rules to specific objects and situations. Jewish thinkers through the ages have speculated about the rationale for this prohibition, or have classified it as an unexplained or mysterious ordinance; however, the Mishnah and talmudic works deal with the technicalities of deriving and applying the law and not with its purpose.

R. Moses Nehemiah ben Shalom Feibush Kahanov (1817–1883) was a Jerusalem talmudist. He was born in Belorussia but after his marriage at the age of 15, settled in Petrovice where at the age of 18 he was appointed assistant to the local rabbi. Some years later, he became rabbi of Khaslavich, a city noted for its scholars. In 1864 he set out for Jerusalem. On his arrival, after a journey of six months, he was appointed head of the Eẓ Ḥayyim yeshivah, the most important in Jerusalem, remaining in this position until his death. Kahanov was remarkably progressive for his time and environment. He appealed for the founding of industrial enterprises, a daring proposal for that time. He even consented to the proposal of Sir Moses Montefiore to introduce the teaching of the vernacular, Arabic, in his yeshivah, but was obliged to abandon the proposal in the face of pressure from extremist elements. One of the first of the old yishuv to speak only Hebrew, he was also one of those who encouraged settlement outside the walls of the Old City of Jerusalem, building a house for himself in Nahlat Shivah. Among his publications were Ereẓ Ḥefeẓ (1884), on laws of terumah and tithes; Hukkot Olam (1886), on mixed species (kilayim ); Mei Menuhot (c. 1860) on the laws of the sabbath, to which was appended Palgei Mayim, giving rules for those traveling by ship on the sabbath; and Netivot ha-Shalom on the Shulḥan Arukh (pt. 1 (1858, 18752), pt. 2 (1861)). He applied himself particularly to the question of the application of the laws of the sabbatical year which had become of practical importance with the establishment of the Jewish agricultural colonies, and in this connection published Shenat ha-Sheva (1881). The eulogies he delivered on the deaths of Baron Asher Rothschild and Sir Moses Montefiore were published. His Sha'alu Shelom Yerushalayim (1867) on the state of Jerusalem and its citizens was published three times. His will was published in 1968 (Siftei Yeshenim, Jerusalem) together with a responsum on Jerusalem and a brief biography.

דף יג,ב-יט,א (ספירה שנייה): "זכרון יעקב... בני בכורי... מו"ה אברהם יעקב ז"ל נפטר כד מרחשון תרמ"ה... כתבתי לב"ב [לבני ביתו] שישלחו לי איזה מכתביו... וקבצתי קבוצות כתבים מחדש"ת... ולקטתי איזה גרגירים מעט מהרבה למען הדפיסם... וקראתי הקונטרס ... זכרון יעקב". דף יט, ב - כ, ב ובעמודים הפנימיים של המעטפת: לקוטים.