The Hajj is an annual pilgrimage to the holy city of Mecca in Saudi Arabia. Muslims are expected to complete the trip at least once in their lifetime, providing they can afford it.
The pilgrims take part in ceremonies, symbolising important parts of the Islamic faith.
Pilgrims prepare for the Hajj by entering into ihram - this is a spiritual state of purity. They must not row or fight with anyone. They also wear special clothes.
Pilgrims take part in several ceremonies, many of which commemorate the trials of the prophet Abraham and his family.
Other ceremonies involve animal sacrifice and cutting your hair.
The Hajj gives Muslims from around the world the chance to come together and worship.
The Hajj begins on the eight day of Dhul-Hijjah - the 12th month of Muslim lunar calendar. In 2004, this fell on 30 January.