More than 1.5 billion Muslims around the world mark the start of Ramadan on June 17, a month of intense prayer, dawn-to-dusk fasting and nightly feasts.
Muslims follow a lunar calendar and a moon-sighting methodology that can lead to different countries declaring the start of Ramadan a day or two apart.
However, this year religious authorities in Saudi Arabia, Egypt, Iran, Indonesia, and most other parts of the world announced based on their sightings of the moon that daily fasting would begin on the same day.
In Pakistan's Federally Administered Tribal Areas and Khyber Pakhtunkhwa Province, Ramadan starts on June 18, a day before the rest of the country.
During Ramadan, observant Muslims abstain from eating, drinking, and sex from sunrise to sunset for the entire month.
A single sip of water or a puff of a cigarette is considered enough to invalidate the fast.
The fast is intended to bring the faithful closer to God and to remind them of the suffering of those less fortunate.
Muslims often give to charities during the month, and mosques and aid organizations organize free meals for the public every night.
Based on reporting by AP, AFP, and RFE/RL's Radio Mashaal