The Islamic Foundation of Ireland has congratulated all Muslims on the beginning of Ramadan, which it says takes place this evening.
The announcement was made today on the foundation's website following a last-minute decision in Saudi Arabia that because the crescent moon had failed to appear there last night, Ramadan could not begin until tomorrow.
Saudi Arabia is where the world's most important Islamic shrines are located.
The Al-Arabiya newspaper is reporting all other Arab counties bar Yemen supported the Saudi decision.
The paper also reports that what it describes as "other Islamic countries" like Indonesia and Malaysia also followed suit.
Ramadan is sacred to Muslims because they believe that it was during that month that the Quran was revealed to the faith's founder, the Prophet Mohammad.
During the 29-30 day-long season Muslims fast from food from dawn until dusk and strive to become more pious and charitable.
They are also obliged to abstain from drinking liquids, smoking and having sex.
The globe's second most popular religion, Islam has many branches.
Together they are estimated by the US-based Pew Research Centre to have a total of 1.6 billion adherents.
This represents 23% of the world's population.
The 2011 census put the number of Muslims living in the Republic of Ireland at 48,130 and an additional 4,000 or so live in Northern Ireland.