Likewise the Apostle Paul also says: But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed [literally, let him be anathema] (Galatians 1:8). Inasmuch as this is true, and attested unto us, rejoicing over this, as one that has found great spoil, we receive the divine canons with delight, and we maintain wholly and unshakably the enactment of these canons set forth by the all­praised Apostles, the holy trumpets of the Spirit, and by the six holy Ecumenical Synods, and those assembled locally to issue such commandments, and by our holy Fathers. For they all, being enlightened by one and the same Spirit, ordained what is beneficial. And whomever they give over to anathema, those we also anathematize; and whomever to expulsion, those we also expel, and whomever to excommunication, those we also excommunicate; and whomever they subject to penances, those we likewise subject.  Canon I of the Seventh Ecumenical Synod

Links From Orthodox Sources

The Canonical Tradition of the Orthodox Church - The Greek Orthodox Archdiocese of America

The Rudder - Canons of The Orthodox Church - Christian Classics Ethereal Library

 Recommended Further Reading