The document itself bears many marks of an early date: --
(1) Its simplicity, almost amounting to childishness, not only discountenances all idea of forgery, but points to the sub-apostolic age, during which Christianity manifested this characteristic. The fact is an important one in the discussion of the canon of the New Testament.
(2) The undeveloped Christian thought, as well as the indications of undeveloped heresy,  confirms this position. Christianity was at first a life, for which the Apostles furnished a basis of revealed thought. But the Christians of the sub-apostolic age had not consciously assimilated the thought to any large extent, while their ethical striving was stimulated by the gross sins surrounding them. 
(3) The Church polity indicated in the Teaching is less developed than that of the genuine Ignatian Epistles, and shows the existence of extraordinary travelling teachers ("Apostles" and "Prophets," chap. xi.). This points to a date not later than the first half of the second century, probably as early as the first quarter. 
Most of these phenomena would, however, consist with a date as late as that of the Ignatian Epistles on the theory that the Teaching was written for a community of Christians in some obscure locality. But this theory must admit that there existed for a long time great variety of Church polity and worship.  Of this there is, indeed, considerable evidence. The undeveloped form of the doctrinal elements of the work constitutes the most serious objection to the theory of a late origin. On the other hand, it seems on many accounts improbable that the work, in its present form, was written earlier than the beginning of the second century: (1) Such a document would not be penned during the lifetime of any of the Apostles. (2) There is no allusion in chap. xvi. to the destruction of Jerusalem. If the author was a Jewish Christian, as seems most probable, such silence implies an interval of at least one generation. (3) The position of the document in the Codex is after the Clementine Epistles, and before the Ignatian. This probably marks the chronological position. (4) The extreme simplicity scarcely consists with the view that the author was nearly contemporary with the Apostles.
Bryennios and Harnack assign, as the date, between 120 and 160; Hilgenfeld, 160 and 190; English and American scholars vary between a.d.80 and 120. Until the priority to Barnabas is more positively established, the two may be regarded as of the same age, about 120, although a date slightly later is not impossible. All attempts to discover the author are, with our present lack of data, necessarily futile. Even the region in and for which it was composed cannot be determined. Jewish-Christian tendencies are not sufficiently indicated to warrant the assumption of a polemical aim.  The document has been assigned to Alexandria, to Antioch, to Jerusalem; indeed, many other places have been named. In favour of the Syrian origin is the literary connection with the Apostolic Constitutions, while the correspondences with the Epistle to Barnabas suggest Egypt as the locality. If the Teaching and Barnabas have a common basis, e.g., the Duæ Viæ, the last may be assigned to Egypt, and the Teaching, in its present form, to Syria. The Palestinian origin is urged by those who lay stress upon the absence of Pauline doctrine in the Teaching [If meant for catechumens only, this fact is sufficiently accounted for.]
The question is still an open one.
As regards the doctrine, polity, usages, and ethics expressed and implied in the Teaching, the reader can judge for himself. The writer is of the opinion that the work represents, on many of these points, only a very small fraction of the Christians during the second century, and that, while it casts some light upon usages of that period, it cannot be regarded as an authoritative witness concerning the universal faith and practice of believers at the date usually assigned to it. The few notices of it, and its early disappearance, confirm this position. The theory of a composite origin also accords with this estimate of the document as a whole.
The version of the Teaching here given is that of Professor Isaac H. Hall and Mr. John T. Napier, which first appeared in the Sunday-School Times (Philadelphia), April 12, 1884. It is now republished by permission of the editor of that periodical and of the joint authors. A few slight changes have been made, some of them in accordance with suggestions from Professor Hall, others to indicate correspondences with book vii. of Apostolic Constitutions.
The division of verses agrees with that of Harnack as given by Schaff. The headings to the chapters have been inserted by the editor. The Scripture references have been selected and verified. The notes have been kept within narrow limits. They serve to indicate the relation of the matter to that in other early writings, mainly the Apostolic Constitutions, and to give various readings and renderings. Occasionally explanations and comments have been inserted. In dealing with this, as with most other books, the best method of study is historico-exegetical. To read the book intelligently is better than to read about it. The editor has sought to furnish some help in this method.
 For the various dates, see p. 375.  [Note this mark of a possibly corrupted source.]  [See Apostolic Fathers, passim.]  [Compare Revelation 2:2 and 9.]
 [Note this mark of a possibly corrupted source.]
 [See Apostolic Fathers, passim.]
 [Compare Revelation 2:2 and 9.]