Sacred tradition is a theological term used in major Christian traditions, primarily those claiming apostolic succession, such as the Catholic, Eastern Orthodox, Oriental Orthodox, Assyrian, and Anglican traditions, to refer to the foundation of the doctrinal and spiritual authority of Christianity and of the Bible.
Christians believe that the teachings of Jesus and the Apostles were preserved in the scriptures as well as by word of mouth and were handed on. This perpetual handing on of the tradition is called the "Living Tradition"; it is believed to be the faithful and constant transmission of the teachings of the Apostles from one generation to the next. That "includes everything which contributes towards the sanctity of life and increase in faith of the People of God; and so the Church, in her teaching, life and worship [the Creeds, the Sacraments, the Magisterium, and the Holy Sacrifice of the Mass], perpetuates and hands on to all generations all that she herself is, all that she believes." The Deposit of Faith (Latin: fidei depositum) refers to the entirety of divine revelation. According to Roman Catholic theology, two sources of revelation constitute a single "Deposit of Faith", meaning that the entirety of divine revelation and the Deposit of Faith is transmitted to successive generations in scripture and sacred tradition (through the teaching authority and interpretation of the Church's Magisterium (which consists of the Church's bishops, in union with the Pope), typically proceeding synods and ecumenical councils).
In Eastern Orthodox theology, sacred tradition is the inspired revelation of God and catholic teaching (Greek katholikos, "according to the whole") of the Church, not an independent source of dogmatic authority to be regarded as a supplement to biblical revelation. Tradition is rather understood as the fullness of divine truth proclaimed in the scriptures, preserved by the apostolic bishops and expressed in the life of the Church through such things as the Divine Liturgy and the Holy Mysteries (Eucharist, baptism, marriage, etc.), the Creed and other doctrinal definitions of the First seven ecumenical councils, canonical Christian iconography, and the sanctified lives of godly men and women.
According to the Christian theological understanding of these Churches, scripture is the written part of this larger tradition, recording (albeit sometimes through the work of individual authors) the community's experience of God or more specifically of Jesus. Thus, the Bible must be interpreted within the context of sacred tradition and within the community of the church. That is in contrast to many Protestant traditions, which teach that the Bible alone is a sufficient basis for all Christian teaching (a position known as sola scriptura).
The word tradition is taken from the Latin trado, tradere, meaning "to hand over, to deliver, to bequeath". According to Catholic theology, 2 Thessalonians 2:15, Paul exhorted the faithful to "keep the traditions that we taught you, whether by word of mouth or by letter." Paul's letters form part of Sacred Scripture; what he passed on "by word of mouth" is part of Sacred Tradition, handed down from the apostles. Both are the inspired word of God; the latter helps to inform understanding of the former. Sacred Tradition can never be in conflict with Sacred Scripture. Protestants note that the verse says either by the word of mouth or by letter, but not that one interprets the other. They also emphasize the reference to "we" in the passage as coming directly from the mouth of the apostles. 
Among the earliest examples of the theological appeal to tradition is the response of early orthodox Christianity to Gnosticism, a movement that used some Christian scripture as the basis for its teachings. Irenaeus of Lyons held that 'rule of faith' ('κανών της πίστης') is preserved by a church through its historical continuity (of interpretation and teaching) with the Apostles. Tertullian argued that although interpretations founded on a reading of all Holy Scripture are not prone to error, tradition is the proper guide. Athanasius held that Arianism fell into its central error by not adhering to tradition.
For the Orthodox Christian, there is one Tradition, the Tradition of the Church, incorporating the Scriptures and the teaching of the Fathers. As explained by Athanasius of Alexandria, "Let us look at the very tradition, teaching, and faith of the catholic Church from the very beginning, which the Logos gave (edoken), the Apostles preached (ekeryxan), and the Fathers preserved (ephylaxan). Upon this the Church is founded (tethemeliotai)"(St. Athanasius, "First Letter to Serapion", 28)
Sacred tradition for the Eastern Orthodox is the deposit of faith given by Jesus to the apostles and passed on in the Church from one generation to the next without addition, alteration, or subtraction. Vladimir Lossky described tradition as "the life of the Holy Spirit in the Church." It is dynamic in application yet unchanging in dogma. It is growing in expression yet is always the same in essence. Rather, Orthodox believe tradition is that faith once delivered as understood within the context of lived history. Tradition is a gift of the Holy Spirit, a living experience, which is relived and renewed through time. Fr. Georges Florovsky wrote
"Tradition is not a principle striving to restore the past, using the past as a criterion for the present. Such a conception of tradition is rejected by history itself and by the consciousness of the Orthodox Church. Tradition is the constant abiding of the Spirit and not only the memory of words. Tradition is a charismatic, not a historical event". (Florovsky, Georges. "The Catholicity of the Church" in Bible, Church, Tradition, p. 47)
The Catholic Church views tradition in much the same terms, as a passing down of that same apostolic faith, but, in a critical difference from the Eastern Orthodox position, Catholicism holds that the faith once delivered, the understanding of it continues to deepen and mature over time through the action of the Holy Spirit in the history of the Church and in the understanding of that faith by Christians, all the while staying identical in essence and substance. Moreover, the understanding may continue to grow and be enriched in the future, not only through mystical experience, but through the practice of the sciences of philosophy and theology as guided by the Holy Spirit; exemplified, for instance, by the Scholastics such as Saint Thomas Aquinas, Duns Scotus, and William of Ockham in the High Middle Ages. A common metaphor used to explain this position is that of a seed: the acorn itself has neither branches nor leaves, yet once planted in fertile soil, it gradually grows into a tall oak; throughout its lifetime, however, it ever continues to be the same tree that was planted.
In the area of moral theology, Mark D. Jordan said that medieval texts appeared to be inconsistent. According to some, prior to the sixth century, the Church's teachings on morality were incoherent. According to John T. Noonan, "history cannot leave a principle or a teaching untouched; every application to a situation affects our understanding of the principle itself."
Sacred Tradition and Sacred Scripture form one sacred deposit of the word of God, committed to the Church. Holding fast to this deposit the entire holy people united with their shepherds remain always steadfast in the teaching of the Apostles, in the common life, in the breaking of the bread and in prayers (see Acts 2, 42, Greek text), so that holding to, practicing and professing the heritage of the faith, it becomes on the part of the bishops and faithful a single common effort.
But the task of authentically interpreting the word of God, whether written or handed on, has been entrusted exclusively to the living teaching office of the Church, whose authority is exercised in the name of Jesus. This teaching office is not above the word of God, but serves it, teaching only what has been handed on, listening to it devoutly, guarding it scrupulously and explaining it faithfully in accord with a divine commission and with the help of the Holy Spirit, it draws from this one deposit of faith everything which it presents for belief as divinely revealed.
It is clear, therefore, that Sacred Tradition, Sacred Scripture and the teaching authority of the Church, in accord with God's most wise design, are so linked and joined together that one cannot stand without the others, and that all together and each in its own way under the action of the one Holy Spirit contribute effectively to the salvation of souls.
Thus, all of the teachings of the Catholic Church come from either Tradition or Scripture, or from the magisterium interpreting Tradition and Scripture. These two sources, Tradition and Scripture, are viewed and treated as one source of Divine Revelation, which includes both the deeds of God and the words of God:
This plan of revelation is realized by deeds and words having in inner unity: the deeds wrought by God in the history of salvation manifest and confirm the teaching and realities signified by the words, while the words proclaim the deeds and clarify the mystery contained in them. (Dei verbum, 2)
The magisterium has a role in deciding authoritatively which truths are a part of sacred tradition.
Most Protestant denominations claim that the Bible alone is the source for Christian doctrine. This position does not deny that Jesus or the apostles preached in person, that their stories and teachings were transmitted orally during the early Christian era, or that truth exists outside of the Bible. For sola scriptura Christians today, however, these teachings are preserved in the Bible as the only inspired medium. Since in the opinion of sola scriptura Christians, other forms of tradition do not exist in a fixed form that remains constant in its transmission from one generation to the next and cannot be referenced or cited in its pure form, there is no way to verify which parts of the "tradition" are authentic and which are not.
Scholars such as Craig A. Evans, James A. Sanders, and Stanley E. Porter have studied how sacred tradition in the Hebrew Bible was understood and used by New Testament writers to describe Jesus.
The Anglican Church does accept apostolic tradition, which can be found in the writings of the early Church Fathers, the decrees of the seven Ecumenical Councils, the Creeds, and the liturgical worship of the Church.