The epistle of Polycarp.

Counted among the apostolic fathers.

Attributed author(s).
Polycarp.

Text(s) available.
On site: Epistle to the Philippians 1-14 (Greek only).
Skeptik (Greek only).
Christian Hospitality Archives: Epistle of Polycarp, very large file in .pdf (Greek only).
CCEL: Polycarp (Greek only).
Early Christian Writings: Polycarp (English only).

Useful links.
Polycarp at Early Christian Writings.
Polycarp in the Catholic Encyclopedia.

Measure for measure (Polycarp to the Philippians 2.3a).

One epistle of Polycarp is extant, that to the Philippians, written but not entirely preserved in Greek. Chapters 10-12, 14, and the last line of 13 are preserved only in Latin.* This epistle is reckoned among the apostolic fathers.

* My thanks to Duane Larrieu for pointing out a typo, now corrected, in the range of chapters preserved in Latin.

Manuscripts.

According to Bart Ehrman (on page 330 of volume 1 of the Loeb edition of the apostolic fathers) and Michael Holmes (on pages 121-122 of The Apostolic Fathers) the following manuscripts are extant for the epistle of Polycarp:

Greek manuscripts (G), nine in number,* century XI and later, noted as v, o, f, p, c, t, n, s, a.
Latin manuscripts (L), nine in number, noted as r, t, c, b, o, p, f, v, m.
Syriac fragments of chapter 12.

* The nine Greek manuscripts all derive from the same exemplar, and all break off at Polycarp 9.2 in the middle of a sentence, at the words και δι υμας υπο. Each then proceeds with Barnabas 5.7, at the words τον λαον τον καινον.