Sifrei is a halakhic Midrash to the books of Numbers and Deuteronomy. As early as amoraic times the word sifrei was employed as the designation for a collection of halakhic beraitot (Meg. 28b; Hag. 3a; Kid. 49b; Shevu. 41b), and also used for a collection of beraitot containing halakhot derived from exegesis of biblical verses (in Deut., Sanh. 85b–86a; cf. BB 124, bi-she'ar sifrei de-Vei Rav; and in Lev., Yoma 74a, "bi-she'ar sifrei de-Vei-Rav"). The Babylonian geonim, and following them some French and German rishonim, designate under the general term sifrei the Mekhilta (or Mekhiltot) to Exodus together with the Sifrei to both Numbers and Deuteronomy. Some of the scholars of North Africa, however, and following them most medieval scholars, limited the name to the works on Numbers and on Deuteronomy.

Since it would appear that the Sifrei both to Numbers and to Deuteronomy in their present form were unknown to either the Jerusalem or the Babylonian Talmuds, it is probable that they were arranged and edited in Erez Israel, but not before the end of the fourth century C.E. The Sifrei to Numbers was first printed together with the Sifrei to Deuteronomy in Venice in 1545, and has been frequently reprinted. It was the fact of their being printed together, in addition to the common name, which caused them to be regarded as one Midrash, but they belong to different tannaitic schools and are therefore treated separately. Like the Sifra, the Sifrei is written in pure mishnaic Hebrew with an admixture of Greek words.

מעבר לשער: התנצלות המגיה... משה הירש בן כה' שמעון פארנבך ז"ל מפיורדא ולע"ע בק"ק זולצבך.

הסכמות: ר' פינחס הלוי איש הורויץ, זקינו של המביא לבית הדפוס, פ"פ דמיין, שושן פורים [טו אדר] תקס"ב; ר' מרדכי בנעט, נ"ש [ניקלשבורג], ב דראש-חודש טבת תקס"ב.