Islam has relatively few holidays compared to most other religions, but those sacred days and times are very important to Muslims. Most Islamic holidays commemorate events in the life of the prophet Muhammad, are special days founded by him, and/or are commanded by the Qur'an.
Muslims observe two major festivals ('Id Al-Fitr and 'Id Al-Adha) and one month of daytime fasting (Ramadan). These are public holidays in Muslim countries. There is also a day of voluntary fasting: 'Ashura, which is also an important Shiite festival.
The popular festival of Mawlid an-Nabi celebrates the birthday of the prophet Muhammad, but is frowned upon as an idolatrous innovation by conservative Muslims.