Muslims have two major religious observances each year, Ramadan and Hajj, and corresponding holidays connected with each one. All Islamic holidays are observed according to the lunar-based Islamic calendar. (See below for 2017 and 2018 calendar dates.)
Ramadan
Each year, corresponding with the ninth month of the lunar calendar, Muslims spend a month in daytime fasting, during the 9th month of the Islamic calendar, called Ramadan.
From dawn to sunset during this month, Muslims abstain from food, liquids, smoking, and sex. Observing this fast is an extremely important aspect of the Muslim faith: in fact, it is one of the Five Pillars of Islam.
Laylat al-Qadr
Towards the end of Ramadan, Muslims observe the "Night of Power," which is when the first verses of the Qur'an were revealed to Muhammad.
Eid al-Fitr
At the end of Ramadan, Muslims celebrate "The Festival of Fast-Breaking." On the day of Eid, fasting is prohibited. The end of Ramadan is generally celebrated by a ceremonial fast-breaking, as well as the performance of the Eid prayer in an open, outdoor area or Mosque.
Hajj
Each year during the 12th month of the Islamic calendar, millions of Muslims make an annual pilgrimage to Mecca, Saudi Arabia, called Hajj.
Day of Arafat
During the 9th day of the Hajj, the holiest day in Islam, pilgrims gather at the Plain of Arafat to seek God's mercy, and Muslims elsewhere fast for the day.
Muslims around the world gather at mosques for a solidarity prayer.
Eid al-Adha
At the end of the annual pilgrimage, Muslims celebrate "The Festival of Sacrifice." The festival includes a ritual sacrifice of a sheep, camel, or goat, an action meant to commemorate the trials of the Prophet Abraham.
Other Muslim Holy Days
Other than these two major observances and their corresponding celebrations, there are no other universally-observed Islamic holidays.
Some Muslims acknowledge other events from Islamic history, which are considered holidays by some but not all Muslims:
Islamic New Year: 1 Muharram
Al-Hijra, the 1st of Muharram, marks the beginning of the Islamic New Year. The date was chosen to commemorate Muhammad's hijra to Medina, a key moment in Islamic theological history.
Ashura: 10 Muharram
The Ashura marks the anniversary of Husein, the grandson of Muhammad. Celebrated mainly by Shi'ite Muslims, the date is commemorated by fasting, blood donation, performances, and decorations.
Mawlid an-Nabi: 12 Rabia' Awal
Mawlid al-Nabim, celebrated on the 12th of Rabiulawal, marks the birth of Muhammad in 570. The holy day is celebrated in different ways by different Islamic sects. Some Muslims choose to commemorate Muhammad's birth with gift-giving and feasts, while others condemn this behavior, arguing that it is idolatrous.
Isra' & Mi'raj: 27 Rajab
Muslims commemorate Muhammad's journey from Mecca to Jerusalem, followed by his ascent to heaven and return to Mecca, on the two holy nights of Isra' and Mi'raj. Some Muslims celebrate this holiday by offering prayer, although there is no specific or required prayer or fast to go alongside the holiday.

Holiday Dates for 2017 and 2018
Islamic dates are based on a lunar calendar, so corresponding Gregorian dates may vary by 1 or 2 days from what is predicted here.
Isra' & Mi'raj:
• Monday, April 24, 2017
• Friday, April 14, 2018
R amadan:
• Saturday, May 27 to Sunday, June 25, 2017
• Wednesday, May 16 to Thursday, June 14, 2018
Eid al-Fitr
• June 25, 2017
• June 15, 2018
Hajj:
• Wednesday, August 30 to Monday, Sept. 4, 2017
• Sunday, August 19 to Friday, August 24, 2018
Day of Arafat:
• Wednesday, August 30, 2017
• Monday, August 20, 2018
Eid al-Adha:
• Friday, September 1 to Tuesday, September 5, 2017
• Tuesday, October 21 to Saturday, October 25, 2018
Islamic New Year 1438 AH.
• Thursday, September 21, 2017
• Tuesday, September 11, 2018
Ashura:
• Friday, September 29, 2017
• Thursday, September 20, 2018
Mawlid an-Nabi:
• Thursday, November 30, 2017
• Tuesday, November 20, 2018