The sign of the cross is a ritual blessing made by members of some branches of Christianity. This blessing is made by the tracing of an upright cross or + across the body with the right hand, often accompanied by spoken or mental recitation of the trinitarian formula.
The sign of the cross is made by touching the hand sequentially to the forehead, lower chest or stomach, and both shoulders, accompanied by the Trinitarian formula: at the forehead In the name of the Father (or In nomine Patris in Latin); at the stomach or heart and of the Son (et Filii); across the shoulders and of the Holy Spirit/Ghost (et Spiritus Sancti); and finally: Amen. The movement is the tracing of the shape of a cross in the air or on one's own body, echoing the traditional shape of the cross of the Christian Crucifixion narrative. There are two principal forms: onethree fingers, right to leftis exclusively used in the Eastern Orthodox Church and the Eastern Catholic Churches in the Byzantine and Chaldean traditions; the otherleft to right, other than three fingersis the one used in the Latin (Catholic) Church, Anglicanism, Methodism, Presbyterianism, Lutheranism and Oriental Orthodoxy (see below). The ritual is rare within other Christian traditions.

The Trinity is a Christian doctrine, stating that God is one Being Who exists, simultaneously and eternally, as a mutual indwelling of three persons (not to be confused by "person"): the Father, the Son (incarnate as Jesus of Nazareth), and the Holy Spirit. Since the 4th century, in both Eastern Christianity and Western Christianity, this doctrine has been stated as " three persons in one God," all three of whom, as distinct and co-eternal persons, are of one indivisible Divine essence, a simple being. The doctrine also teaches that the Son Himself has two distinct natures, one fully divine and the other fully human, united in a hypostatic union. Support of the doctrine of the Trinity is known as Trinitarianism. Most denominations within Christianity are Trinitarian, and regard belief in the Trinity as a mark of Christian orthodoxy.