The Two Ways (also known as The Teaching or The Teaching of the Apostles)
The Two Ways is very likely the oldest early Christian writing outside of the New Testament. It was possibly written before some of the later books of the New Testament. It is a description of the way of life and the way of death. It has survived in three forms: 1. it is the first part of the document which has come to be known as The Didache; 2. it is contained in the last part of The Letter of Barnabas; 3. it exists on its own in a Latin version which is probably a translation from Greek.
To read English translations the first two versions of The Two Ways, see the links above. To read an English translation of the Latin verion, see The Apostolic Fathers: An American Translation. This book by Edgar J. Goodspeed contains a comparision of the three forms of The Two Ways.