Muslims begin observing the holy month of Ramadan Saturday in many parts of the world. They believe this is the time when God revealed the holy Qu'ran to the Prophet Mohammad.
During Ramadan, Muslims refrain from food and drink during daylight hours.
U.S. President Barack Obama has extended "best wishes" to the Muslim community at home and abroad. He said he is looking forward to welcoming Muslim Americans to the White House for an iftar dinner -- the evening meal that breaks the fast.
Ramadan this year coincides with the World Cup. There are dozens of Muslim players in the tournament who face the challenge of being properly hydrated and getting enough nutrition before sunrise to carry them though a strenuous football (soccer) game in Brazil's heat.
FIFA's chief medical officer said earlier this week if players follow Ramadan "appropriately," there should be "no reduction" in their physical performances.
Muslims can also seek an exemption from fasting during Ramadan for a more opportune time.
Some Muslim athletes were granted exemptions by their religious leaders for the 2012 Olympics in London.
The start of Ramadan is determined by the sighting of a crescent moon with the naked eye. In the United States and southern Canada the holy month will begin Sunday, June 29.