Codex Campianus is a Greek uncial manuscript of the New Testament Gospels, written on parchment. It is designated as "M" or "021" in the Gregory-Aland numbering of New Testament manuscripts, and ε 72 in the von Soden numbering of New Testament manuscripts. Using the study of comparative writings styles (palaeography), it has been assigned to the 9th century CE.

The manuscript has complex contents. It has marginal notes and was prepared for liturgical (religious) use. It contains musical notation surrounding some of the text, with a Harmony of the Gospels included at the bottom of each page. Art miniatures are included of the respective evangelists before each Gospel.

The text of the manuscript was held in high esteem by some 19th-century scholars, but this general opinion changed in the 20th century; as a result the manuscript is rarely cited in critical editions of the Greek New Testament.

The manuscript is a codex (the precursor to the modern book), containing a complete text of the four Gospels, on 257 parchment leaves (sized 22 cm by 16.3 cm); the text is written in two columns per page, 24 lines per column, in brown ink. The leaves are arranged in quarto (this being four parchment leaves placed on top of each other and folded in half), and according to Biblical scholar Frederick H. A. Scrivener, it is written in a "very elegant and minute uncial" script. The letters are similar in style and look to those from Codex Mosquensis II (V). The breathing marks (utilised to designate vowel emphasis) and accents (used to indicate voiced pitch changes) have been added in red ink, along with some musical notation. Lines for which the text is to be written were drawn with a sharp point, and the letters are written on the line, as opposed to being suspended under. A middle point is used as a phrase mark.

Quotations from the Old Testament are indicated, with miniature pictures of the four Evangelists before each Gospel, with Mark, Luke, and John all sat down. Ornamentations are included at the beginning of each Gospel, decorated in red and blue ink, and the larger initials of each section are also ornamented in red and blue ink. Beginning (ἀρχή / arche) and ending (τέλος / telos) marks used for the weekly lection readings of the Church's calendar are also written. The liturgical notes in the margin are written in minuscule letters. According to Biblical scholar Constantin von Tischendorf, the handwriting of the liturgical notes in the margin is very similar to the Oxford manuscript of Plato dated to the year 895 and housed at the Bodleian Library.

The manuscript has a number of errors due to contemporary changes in the pronunciation of Greek, a phenomenon known as iotacism. It has errors of final nu (this being the inclusion of the Greek letter ν/n after certain verbs before a following word starting with a vowel, or the omission of the ν/n before a word starting with a consonant). The text of the Gospels is divided according to the Ammonian Sections and the Eusebian Canons (both early divisions of the gospels into sections). It has a Harmony of the Gospels written at the bottom of the pages.

Besides the New Testament text, it contains a Chronology of the Gospels, the Epistle to Carpianus, the Eusebian Canon tables, liturgical books with the Synaxarion and Menologion hagiographies, αναγνώσματα (anagnosmata / notes of the Church Lessons), with the titles of the chapters (known as τίτλοι / titloi) written at the top of the pages. There is some Arabic text on the last leaf, and a note in Slavonic which no one appears to have provided a translation for nor noted its location in the manuscript. The Arabic note is illegible except for one word, "Jerusalem". Some notes are written in very small letters.

The Greek text of the codex is considered a representative of the Byzantine text-type, with a number of Caesarean readings. The text-types are groups of different New Testament manuscripts which share specific or generally related readings, which then differ from each other group, and thus the conflicting readings can separate out the groups. These are then used to determine the original text as published; there are three main groups with names: Alexandrian, Western, and Byzantine. Tischendorf states its text is close to Codex Cyprius (K). The textual critic Hermann von Soden describes its text is a result of Pamphilus of Caesarea's recension. It has a similar text to the minuscules 27, 71, 692, and 1194, indicating it is one of the manuscripts in Family 1424.