The priest wears the epitrachil whenever serving as a priest (as opposed to simply attending a service). For some services, e.g. vespers or matins, he wears the epitrachil by itself. When he is fully vested for the Divine Liturgy, he wears the epitrachil over the sticharion and under the zone and the phelonion. If a priest is simply attending a service, he wears no vestments, but will put on his epitrachil (and often his epimanikia) before receiving the Eucharist. When the bishop is fully vested he wears the epitrachil over the stikhar and under the zone, the sakkos and the omophor.