The procession as a practice of the Christian Church originates in the triumphal entry of Jesus into Jerusalem. All four evangelists record the event and all four make mention of the hosannas and acclamations of the people which accompanied it.[1] True, the procession is older than Christianity and wider in observance. It seems to be a natural impulse of humanity in all ages and in all lands to make orderly progress from one place to another for the expression of communal joy or lamentation or to seek the aid and blessing of supernatural power in the activities and vicissitudes of life. Processional ceremonies as they were observed in ancient oriental civilizations or in the culture of Greece and Rome are not considered here, except as they may have affected Christian origins. The purpose of this chapter is to describe the background and setting of processional forms which, in their evolution, gave rise to a continuity of hymns; to trace the origin, development and distinguishing features of such processional hymns in the Middle Ages and to display processional hymnody in its distinctive character as a separate category of medieval Latin hymnology. Prior to the fourth century the record is obscure. Miscellaneous notices begin to appear in the last quarter of the century. Basil notes a procession in the form of a litany (c. 375). Ambrose mentions a procession of monks (c. 388) and also refers to a procession in Rome honoring Sts. Peter and Paul, in his hymn, _Apostolorum passio_, “The passion of the Apostles,” (A. H. 50. 17). Chrysostom was active in organizing processions in Constantinople to offset Arian influence (390-400).[2] At the same period, 379-388, Aetheria (St. Sylvia of Aquitania?) made her pilgrimage to the holy places of Palestine, describing in her journal in detail, the ceremonies enacted in the worship of the Christian Church at Jerusalem.[3] Remarkable in all respects, Aetheria’s narrative is obviously written in a spirit of devotion with eager curiosity and joyful appreciation. She describes, among other observances, the Hour services, especially the _lucernare_ when hymns were sung, the Sunday procession to the Anastasis or Church of the Resurrection which marked the tomb of Jesus and the procession and rites for the Feasts of the Epiphany, Ypapanti or Presentation of Christ in the temple, Palm Sunday and Easter.[4] Hymns in which the laity as well as the clergy participated are mentioned in connection with these ceremonies but no specific hymn is named. The immediate purpose of the processions at Jerusalem appears to have been the enactment of scenes in the life of Jesus in the places where they occurred, introducing a dramatic element which pervades medieval processional observances throughout their history.