Eid - as it is commonly known - is one of the biggest celebrations in the Muslim calendar.
What is Eid al-Fitr?
Eid takes place at the end of Ramadan - a month of prayer and fasting.
The name "Eid al-Fitr" translates as "the festival of the breaking of the fast".
Like the beginning of Ramadan, Eid begins with the first sighting of the new moon.
For most Muslims in the UK, this will be on the evening of 12 May.
What happens at Eid?
Many Muslims will attend Eid prayers at their mosque, early on 13 May.
In the Middle East, these are held straight after the Fajr morning prayer. In the UK, it's any time from 07:00 onwards.
It's a tradition to wear new clothes and on the way to the mosque, eat something sweet such as a date, and recite a small prayer called a takbeer.
Before Eid prayers, Muslims are also required to pay an amount to charity per household called zakaat al fitr to help feed the poor.
Many people enjoy large meals with friends and family, and exchange money and gifts - in many countries, Eid al-Fitr is a public holiday.
If you want to wish someone well at Eid, the greeting is "Eid Mubarak".
Eid celebrations in south London, 2016
What impact will lockdown have?
Lockdown restrictions are due to ease in England, Scotland and Wales from Monday 17 May, but the government has said there will be no early exemption for Eid.
What is Ramadan?
Ramadan is the Arabic name for the ninth month in the Islamic calendar.
It is considered one of the holiest Islamic months.
It's also one of the Five Pillars of Islam. These are five principles which Muslims believe are compulsory acts ordered by God.
Muslims believe that some of the first verses of the Islamic holy book, the Qu'ran, were revealed to the Prophet Muhammad during the month of Ramadan. Extra emphasis is placed on reciting the Qu'ran at this time.
Fasting is considered to be an act of worship, which enables Muslims to feel closer to God and strengthen their spiritual health and self-discipline.
How does this work in practice?
Muslims have an early morning meal before dawn, known as suhoor or sehri.
They break their fast after sunset for the evening meal, called iftar or fitoor.
Ramadan is also a time when Muslims are encouraged to give to charity, strengthen their relationship with God, and show kindness and patience.
During the month, believers also head to the mosque for an additional night prayer called Taraweeh. This is only held during Ramadan.
Taraweeh prayers at a mosque in Cairo
How has Ramadan been different this year?
This is the second Ramadan to have fallen during the coronavirus pandemic.
For Muslims in the UK, just like fellow believers around the world, this has meant another year of changes to traditional practices.
The iftar meal is usually shared with family and friends. Because of the lockdown, such meetings have been restricted once more.
However, while mixing between households was banned during Ramadan in 2020, this year the festival has coincided with the easing of some lockdown rules in England.
Up to six people or two households can currently gather outdoors or in a private garden. Restaurants are also able to serve meals outdoors.
For those who have been unable to meet, many virtual iftar events and online Islamic lectures have taken place.
What else has changed?
Another change from 2020 is that mosques have been open throughout the UK, and able to host Taraweeh prayers in the evening.
Mosques in England are asking worshippers to wear a face covering, bring their own prayer mat, and socially distance.
Many mosques have also reduced the length of prayers to minimise the time spent in congregation.
What are the rules for places of worship?
How are the dates for Ramadan and Eid set?
The Islamic calendar follows the lunar calendar of 12 months.
The month of Ramadan is the ninth of the year, and Eid is celebrated at the beginning of the 10th month, Shawwal.
Each month begins with the sighting of the new crescent moon and lasts either 29 or 30 days.
In the past, this was done by the naked eye, but in recent years, telescopes and technology have been used.
Crescent moon seen over the closed Grand Mosque of Delhi Jama Masjid on the first day of Ramadan on 25 April 2020.
Muslim countries are spread across a large geographical area, from Indonesia to Morocco, meaning that some Muslims may see the new moon earlier than others.
"Traditionally, Makkah [Mecca in Saudi Arabia] was the centre of sighting the moon," says Prof Muhammad Abdel Haleem from the Centre of Islamic Studies at London's SOAS (School of Oriental and African Studies).
"Sometimes even in the Middle East, neighbouring countries will say they've seen the moon on different days," he says.
The lunar calendar is about 10 days shorter than the Western calendar. which means that each year Ramadan starts about 10 days earlier.
Who can fast during Ramadan?
Fasting should only be done by people who are in good health.
Some Muslims are exempt:
Those who are sick or ill and whose health will be affected by fasting
Children - although some may begin to practise fasting from a young age
Pregnant and breastfeeding women
What's Eid al-Adha?
Although Eid al-Fitr has become a well-known event in the UK, this is not the only Eid celebration in the Islamic calendar.
Eid al-Adha is celebrated during the month of Dhul-Hijjah. This is the month where Muslims from across the world make the pilgrimage to Makkah known as Hajj.