The Didache (meaning "Teaching") is a brief early Christian treatise, dated by most scholars to the late first or early 2nd century. The first line of this treatise is "Teaching of the Lord to the Gentiles (or Nations) by the Twelve Apostles."

The text, parts of which constitute the oldest surviving written catechism, has three main sections dealing with Christian ethics, rituals such as baptism and Eucharist, and Church organization. It is considered the first example of the genre of the Church Orders.

The work was considered by some of the Church Fathers as part of the New Testament but rejected as spurious or non-canonical by others, eventually not accepted into the New Testament canon. The Ethiopian Orthodox Church "broader canon" includes the Didascalia, a work which draws on the Didache.

Lost for centuries, a Greek manuscript of the Didache was rediscovered in 1873 by Philotheos Bryennios, Metropolitan of Nicomedia in the Codex Hierosolymitanus. A Latin version of the first five chapters was discovered in 1900 by J. Schlecht. The Didache is considered part of the category of second-generation Christian writings known as the Apostolic Fathers.