Traditionally a period of spiritual reflection, Ramadan this year coincides with the war in Iraq, the ongoing Palestinian-Israeli conflict and harsh economic times in countries like Egypt, the most populous nation in the Arab world.
Millions of Muslims in Egypt, Jordan and Yemen began fasting Sunday. Muslims elsewhere are expected to begin marking Ramadan on Monday because Islamic officials there decreed that the holiday should begin a day later.
Indonesia, the world's most populous Muslim nation, and Iraq will officially begin the fasting month Monday.
Muslims believe it was during Ramadan about 1,400 years ago that the Quran, the Islamic holy book, was revealed to the Prophet Muhammad.
Abdel Hakem Abaed, a Yemeni university student, said he will be "praying to God during Ramadan for the sake of Muslims everywhere in Iraq, Palestine, Afghanistan. This is our task."
In Egypt, Ramadan is usually a festive affair, where strings of colored lights and lanterns brighten streets throughout the capital, Cairo, and in most other centers.
For more than two hours after the first daily fast-breaking meal, or "iftar," on Sunday, Cairo's normally traffic-choked streets were nearly empty as Egyptians sat around dining tables at home or in hotels to feast on meats, salads, rice dishes and desserts.
But Egypt's deteriorating economy, marked by a weak currency and a bread crisis that hit just weeks before Ramadan began, has cast a pall over the holy month, forcing some Muslims to give up some culinary staples because of high prices.
"The country is now like a fatigued old man," said Salem el-Khateeb, a 64-year-old spice shop owner in Khan al-Khalili, a famous market district in the capital.
"Prices of all kinds of nuts and dried apricots have doubled compared to last year. Most people I know are replacing apricots with oranges to make juice for their children. And now I am selling nothing."
Nasser Lashen, who owns a shop selling popular Ramadan lanterns, or "fanous," said prices for the mostly Chinese-made lamps are higher, but "there are various types, so I think people don't have a major problem."
Throughout the city, tables known as "Mawaid el-Rahman," or "banquets of mercy," lined streets, offering passers-by free meals. But the recent bread crisis has even affected this Ramadan icon, with one banquet supervisor, identifying himself as Khalifa, saying there was no bread available for the meal.
In Jordan, where Muslims also completed their first day of fasting Sunday, people said the crises in neighboring Iraq and the Palestinian territories have taken the gloss off this year's Ramadan, which is seen by many as a reflective, festive period.
"Ramadan should be a month of austerity, not a month of lavishness ... (where) instead of spending money on food as if they had never the opportunity to eat, they should think of helping their brothers in Iraq and Palestine," said Amal Salah, a writer of children's stories.
Popular opposition to the U.S.-led war and occupation in Iraq and the Israeli attacks against Palestinians is high in Jordan, a country whose government is a close American ally and has signed a 1994 peace treaty with Israel - one of only three Arab states to do so.
In Iraq and Saudi Arabia, Ramadan eve was overshadowed by a rocket attack that killed one U.S. soldier and injured 15 other people in central Baghdad and a U.S. warning to Americans living in Saudi Arabia to be "particularly vigilant" for terrorist attacks during the holy fasting month.
Monday in Iraq saw even more violence: five suicide bombings in Baghdad which killed at least ten Iraqis, and two separate incidents which killed three American soldiers and wounded four others.
In Saudi Arabia, the custodian of Islam's two holiest shrines, the American Embassy warned its citizens living there that "terrorist groups may place special operational significance on the upcoming month of Ramadan."