The Tosefta follows the Mishnah the way a shadow follows a figure, matching its six orders and nearly all of its tractates while remaining roughly three times its bulk. The relationship between the two works is intimate and uneven. In many passages the Tosefta reads as the earliest commentary on the Mishnah, glossing its terms, supplying the scriptural derivations the Mishnah omits, and naming the sages behind rulings the Mishnah leaves anonymous. In other passages it transmits an alternative tradition altogether, ordering the material differently or ruling the other way, which suggests that both works drew on a common sea of tannaitic teaching and selected from it differently.
The units it preserves are baraitot, teachings of the tannaim that stand outside the Mishnah, and the two Talmuds quote such baraitot constantly, often in wording close to the Tosefta's text. Its language is the same Mishnaic Hebrew, and its halakhic style the same terse case law, but without the Mishnah's disciplined final editing, so that narrative expansions and aggadic material survive in it more generously. Because it was never the curriculum text the Mishnah became, the Tosefta was copied less and studied less, and its two principal manuscripts, Vienna and Erfurt, differ enough to keep its editors busy to this day.