Christmas is marked on the 25 December (7 January for Orthodox Christians).
Christmas is a Christian holy day that marks the birth of Jesus, the son of God.
The story of Christmas
Jesus' birth, known as the nativity, is described in the New Testament of the Bible.
The Gospels of Matthew and Luke give different accounts. It is from them that the nativity story is pieced together.
Both accounts tell us that Jesus was born to a woman called Mary who was engaged to Joseph, a carpenter. The Gospels state that Mary was a virgin when she became pregnant.
In Luke's account Mary was visited by an angel who brought the message that she would give birth to God's son. According to Matthew's account, Joseph was visited by an angel who persuaded him to marry Mary rather than send her away or expose her pregnancy.
Matthew tells us about some wise men who followed a star that led them to Jesus' birthplace and presented him with gifts of gold, frankincense and myrrh. Luke tells how shepherds were led to Bethlehem by an angel.
According to tradition, Joseph and Mary travelled to Bethlehem shortly before Jesus' birth. Joseph had been ordered to take part in a census in his home town of Bethlehem.
All Jewish people had to be counted so the Roman Emperor could determine how much money to collect from them in tax. Those who had moved away from their family homes, like Joseph, had to return to have their names entered in the Roman records.
Joseph and Mary set off on the long, arduous 90-mile journey from Nazareth along the valley of the River Jordan, past Jerusalem to Bethlehem. Mary travelled on a donkey to conserve her energy for the birth.
But when they arrived in Bethlehem the local inn was already full with people returning for the census. The innkeeper let them stay in the rock cave below his house which was used as a stable for his animals.
It was here, next to the noise and filth of the animals, that Mary gave birth to her son and laid him in a manger.
Advent is the period of preparation for the celebration of the birth of Jesus and begins on Sunday nearest to 30th November. The word Advent comes from the Latin adventus meaning coming. Traditionally it is a penitential season but is no longer kept with the strictness of Lent and Christians are no longer required to fast.
Advent wreaths are popular especially in churches. They are made with fir branches and four candles. A candle is lit each Sunday during Advent.
Christmas Day is the Christian festival most celebrated by non-churchgoers, and churches are often completely full for the service late on Christmas Eve.
An important part of today's Christmas is the myth of Father Christmas (called Santa Claus in America). His origins are in Christian and European tradition. But the visual image of Father Christmas that we have today is the one popularised by American card-makers in the Victorian era.
Traditionally, Father Christmas visits houses at midnight on Christmas Eve, coming down the chimney to leave presents. Children hang up stockings - nowadays usually large socks with Christmas patterns knitted into them - for Father Christmas to fill with little toys and presents ('stocking fillers').
Some traditions surrounding Father Christmas pre-date Christianity. His sleigh, pulled by reindeer, is left over from Scandinavian mythology. The practice of leaving mince pies and a glass of milk or brandy for him on Christmas Eve may be a remnant of Pagan sacrifices made to mark the end of winter and the coming of spring.
The USA has the figure of Santa Claus, whose name comes from Saint Nicholas via the Dutch Sinterklaas. Saint Nicholas of Myra (a location in modern-day Turkey) is, among other things, the patron saint of sailors. A famous story has him anonymously delivering bags of gold coins to a man who could not afford dowry for his daughters to get married. Some versions of this story even have Saint Nick dropping the bags down the chimney.
In modern times the figures of Father Christmas and Santa Claus are indistinguishable.