The chief textual witness to the text of the Didache is an eleventh-century Greek parchment manuscript known as Codex Hierosolymitanus (or Codex H) that was discovered in the late nineteenth century, now kept in Jerusalem. The Church Fathers also cite the Didache, so we know it enjoyed a place within early Christian life and practice. Eusebius, for example, places it alongside non-canonical books that “are known to most of the writers of the Church” (Ecclesiastical History 3.25).
In the early twentieth century, two small Greek parchment codex fragments with portions of the Didache turned up in the Egyptian city of Oxyrhynchus. These represent the earliest Greek witness of the Didache by about 650 years, since the fragments are generally dated to the fourth century (and Codex H to the year 1056). In 1922, British papyrologist Arthur Hunt published the edition of the fragments in the famous Oxyrhynchus Papyri series. The fragments are referred to by their publication number, P.Oxy. 15.1782.
Measuring 5 x 5.8 cm and 5.7 x 4.8 cm, the fragments are part of a “miniature codex.” These palm-sized manuscripts apparently became popular among Christians in the fourth century and beyond, and quite a few of them were discovered in the ancient trash heaps at Oxyrhynchus. The Oxyrhynchus fragments preserve the text of Didache 1:3c-4a and 2:7b—3:2a. Hunt calculated that eight leaves were required for the text intervening between folio 1 verso and folio 2 recto. This is of course assuming that the fragments are part of a continuous text of the Didache and not merely extracts. (I personally think it is highly possible that we have here extracts and not a continuous text, but more on that later.)
The fragments are significant for their age but also because they demonstrate variation in wording compared to the text of Codex H. To wrap up this brief summary, I provide below two good photographs of the two Oxhyrhynchus Didache fragments.