Neither the Babylonian Talmud nor the Jerusalem Talmud mention this work under the name "Mekhilta," nor does the word appear in any of the passages of the Talmud in which the other halakhic midrashim, Sifra and Sifre, are named. It seems to be intended, however, in one passage which runs as follows: "R. Josiah showed a Mekhilta from which he cited and explained a sentence." The text quoted by R. Josiah can be found in the extant version of the Mekhilta, Mishpatim.
It is not certain, however, whether the word "mekhilta" here refers to the work under consideration, for it may allude to a baraita collection, which might also be designated a mekhilta.
On the other hand, this midrash, apparently in written form, is mentioned several times in the Talmud under the title She'ar Sifre debe Rav "The Other Books of the Schoolhouse". A geonicresponsum in which appears a passage from the Mekhilta likewise indicates that this work was known as She'ar Sifre debe Rav. The first individual to mention the Mekhilta by name was the author of the Halakhot Gedolot.
The present Mekhilta cannot, however, be the one composed by Ishmael, as is proved by the references in it to Ishmael's pupils and to other later tannaim. Both Maimonides and the author of the Halakhot Gedolot, moreover, refer, evidently on the basis of a tradition, to a much larger Mekhilta extending from Exodus 1 to the end of the Torah, while the midrash here considered discusses only certain passages of Exodus. It must be assumed, therefore, that Ishmael composed an explanatory midrash to the last four books of the Torah, and that his pupils amplified it.
A later editor, intending to compile a halakhic midrash to Exodus, took Ishmael's work on the book, beginning with ch. 12, since the first eleven chapters contained no references to the halakhah. He even omitted passages from the portion which he took, but (by way of compensation) incorporated much material from the other halakhic midrashim, Sifra, the Mekhilta of Rabbi Shimon, and the Sifre to Deuteronomy. Since the last two works were from a different source, he generally designated them by the introductory phrase, "davar aḥer" = "another explanation," placing them after the sections taken from Ishmael's midrash. But the redactor based his work on the midrash of Ishmael's school, and the sentences of Ishmael and his pupils constitute the larger part of his Mekhilta. Similarly, most of the anonymous maxims in the work were derived from the same source, so that it also was known as the "Mekhilta of Rabbi Ishmael." The redactor must have been a pupil of Judah ha-Nasi, since the latter is frequently mentioned.
Barayata from the Mekhilta are introduced in the Babylonian Talmud by the phrases Tana debe R. Yishmael ("It was taught in the school of R. Ishmael"), and in the Jerusalem Talmud and the aggadahs by Teni R. Yishmael ("R. Ishmael taught"). Yet there are many barayata in the Talmud which contain comments on Book of Exodus introduced by the phrase Tana debe R. Yishmael but which are not included in the Mekhilta under discussion. These must have been included in Ishmael's original Mekhilta, and the fact that they are omitted in this midrash is evidence that its redactor excluded many of the passages from Ishmael's work.
The Mekhilta begins with Exodus 12, this being the first legal section found in Exodus. That this is the beginning of the Mekhilta is shown by the Arukh s.v. טמא, and by the Seder Tannaim v'Amoraim. In like manner, R. Nissim proves that the conclusion of the Mekhilta which he knew corresponded with that of the Mekhilta now extant. In printed editions the Mekhilta is divided into nine "massektot," each of which is further subdivided into "parshiyyot". The nine massektot are as follows:
"Massekta de-Pesah", covering the pericope "Bo" (quoted as "Bo"), Exodus 12:1–13:16, and containing an introduction, "petikta," and 18 sections.
"Massekta de-Vayehi Beshalach" (quoted as "Beshallah"), Exodus 13:17–14:31, containing an introduction and 6 sections.
"Massekta de-Shirah," (quoted as "Shirah"), Exodus 15:1–21, containing 10 sections.
"Massekta de-Vayassa," (quoted as "Vayassa"), Exodus 15:22–17:7, containing 6 sections.
"Massekta de-Amalek", consisting of two parts:
the part dealing with Amalek (quoted as "Amalek"), Exodus 17:8–16, containing 2 sections.
the beginning of the pericope "Yitro" (quoted as "Yitro"), Exodus 18:1–27, containing 2 sections.
"Massekta de-Bahodesh," (quoted as "Bahodesh"), Exodus 19:1–20,26, containing 11 sections.
"Massekta de-Nezikin," Exodus 21:1–22:23. (see next)
"Massekta de-Kaspa," Exodus 22:24–23:19; these last two messektot, which belong to the pericope "Mishpatim" contain 20 sections consecutively numbered, and are quoted as "Mishpatim"
"Massekta de-Shabbeta", containing 2 sections:
covering the pericope "Ki Tisa" (quoted as "Ki Tisa"), Exodus 31:12–17
covering the pericope "Vayakhel" (quoted as "Vayakhel"), Exodus 35:1–3
The Mekhilta comprises altogether 77, or, if the two introductions be included, 79 sections. All the editions, however, state at the end that there are 82 sections.
Although the redactor intended to produce a halachic midrash to Book of Exodus, the majority of the Mekhilta is aggadic in character. From Exodus 12 the midrash was continued without interruption as far as Exodus 33:19, i.e. to the conclusion of the chief laws of the book, although there are many narrative portions scattered through this section whose midrash belongs properly to the aggadah. Furthermore, many aggadot are included in the legal sections as well.
The halakhic exegesis of the Mekhilta, which is found chiefly in the massektot "Bo", "Bahodesh", and "Mishpatim" and in the sections "Ki Tisa" and "Vayakhel", is, as the name "mekhilta" indicates, based on the application of the middot according to R. Ishmael's system and method of teaching. In like manner, the introductory formulas and the technical terms are borrowed from his midrash. On the other hand, there are many explanations and expositions of the Law which follow the simpler methods of exegesis found in the earlier halakha.
The aggadic expositions in the Mekhilta, which are found chiefly in "Beshallah" and "Yitro" are in part actual exegesis, but the majority of them are merely interpretations of Scripture to illustrate certain ethical and moral tenets. Parables are frequently introduced in connection with these interpretations  as well as proverbs and maxims. Especially noteworthy are the aggadot relating to the battles of the Ephraimites and to Serah, Asher's daughter, who showed Joseph's coffin to Moses, besides others, which are based on old tales and legends.
Lauterbach, Jacob Z. (1961) [First published 1933], Mekilta de-Rabbi Ishmael: A Critical Edition on the Basis of the Manuscripts and Early Editions with an English Translation, Introduction, and Notes, Philadelphia: Jewish Publication Society.