The Didache, also called The Teaching (or Doctrine) of the Twelve Apostles, is a short treatise that dates back to the early Christian Church and was accounted by some of the Fathers as next to Holy Scripture. It was probably written in Syria during the second half of the 1st century, although some scholars suggest a 2nd-century composition.
The first part of the Didache is a moral treatise describing the Two Ways, the Way of Life and the Way of Death. The second and third parts contain instructions on baptism, the Eucharist, fasting, prayer, matters of church organization, apostles and teachers, prophets, bishops, and deacons. The Didache is perhaps the first text to append a doxology to the Lord's Prayer: "...for thine is the power and the glory unto all ages."
Although partially paraphrased in other ancient documents (see, for example, the Didascalia Apostolorum below), the Didache was practically lost until Philotheos Bryennios , Greek Orthodox metropolitan of Nicomedia, rediscovered/published it in 1873/1883.