In the East, today we celebrate (if we're on the new calendar - 13 days later for the old calendar); the feast of Theophany, the baptism of the Lord. In the West they celebrate Epiphany, the arrival of the three wise men bearing gifts. There is usually some confusion here, especially for new converts to Orthodoxy from traditions that celebrated Epiphany. It's an understandable thing. The words sound alike and they're on the same day. I'm not going to go into this huge discourse on the differences between the two, but here it is in a nutshell:
Theophany is, as I mentioned, the celebration of the baptism of Christ. Some people will wonder why Christ had to be baptized. After all, He is God, right? Right. When Christ entered the waters of the Jordan the water was sanctified.* This is stated in the troparion of the afterfeast. So what does theophany mean? Look at the words of the troparion:
When Thou O Lord wast baptized in the JordanSo on the feast of Theophany, the Trinity - Father, Son and Holy Spirit - was clearly revealed to mankind for the first time. Theophany (theophania) means "appearance of God".
the worship of the Trinity was made manifest;
for the voice of the Father bore witness to Thee
and called Thee His beloved Son.
And the Spirit in the form of a dove,
confirmed the truthfulness of His word.
O Christ our God who hast revealed Thyself
and hast enlightened the world, glory to Thee!
Epiphany is understood as the feast of the revelation of Christ to the Magi who represent the Gentiles. Christ was revealed (Epiphany means "manifestation") to the nations at his birth. It was the culmination of the Nativity.
These two feasts are not really in conflict. Their focus is different but they compliment each other. In the East the worship of the Magi is included in the Nativity feast and in the West there is a separate celebration of the baptism of Christ (instituted rather late, but I'm not sure of the date). The focus in the West seems to be on the revelation of Christ-as-God to the world, beginning his earthly ministry. The focus in the East is on the revelation of Christ as one of the three persons of the Holy Trinity, the Trinity itself manifest for the first time.
*This is why we celebrate the Great Blessing of Waters today (and last night on the Eve). During the blessing of waters, a cross is lowered into the water three times in the same way a baby is lowered into the water during his baptism. The water is sanctified by Christ. Hopefully this makes enough holy water to last all year but if not, a Lesser Blessing of Waters may be performed at almost any time during the year.
For more thorough reading:
- Mystagogy: Epiphany in Eastern and Western Christianity (explains in detail the history of the developments of the feasts in East and West)
- Mystagogy (Great page!): Theophany Resource Page
- Orthodox Wiki: Theophany
- Catholic Culture: Meaning of Epiphany
- Wikipedia: Epiphany
- The Winter Pascha by Fr. Thomas Hopko (available from many sources)