The Orthodox believe that their teachings today are the same as or are in essential harmony with the teaching of the first apostles. This form of the doctrine was formulated by [[Irenaeus of Lyons]] in the second century, in response to certain Gnostics. These Gnostics claimed that Christ or the Apostles passed on some teachings secretly, or that there were some secret apostles, and that they (the Gnostics) were passing on these otherwise secret teachings. Irenaeus responded that the identity of the original Apostles was well known, as was the main content of their teaching and the identity of the apostles' successors. Therefore, anyone teaching something contrary to what was known to be apostolic teaching was not, in any sense, a successor to the Apostles or to Christ.
In addition to a line of historic transmission, Orthodox Christian churches, as also the [[Oriental Orthodox|Non-Chalcedon Orthodox]] churches, additionally require that a [[hierarch]] maintain Orthodox Church doctrine, which is that of the Apostles, as well as communion with other Orthodox bishops. The Orthodox Christians have at times permitted clergy ordained by [[Church of Rome|Roman Catholic]] and Anglican bishops to be rapidly [[ordain]]ed within Orthodoxy. However, this is a matter of [[oikonomia]] and not recognition of Apostolic Succession.