Millions of Muslims are celebrating Eid al-Adha.
It's different from Eid al-Fitr, which was celebrated in June.
Here's everything you need to know about the two Eids and why they're different.
The word 'Eid' means 'feast' or 'festival'. Each year Muslims celebrate both Eid al-Fitr and Eid al-Adha - but the names often get shortened to just 'Eid', which is why it can be confusing.
Eid al-Fitr - which means 'festival of the breaking of the fast - is celebrated at the end of Ramadan, , a month when many adult Muslims fast.
Eid al-Adha - which means 'feast of the sacrifice' - is celebrated just over two months later, at the same time when many Muslims perform the Hajj pilgrimage.
Eid al-Adha coincides with the end of Hajj - the annual Islamic pilgrimage to Mecca in Saudi Arabia, and is generally considered the holier of the two.
Hajj is a once-in-a-lifetime activity that is a duty for those who can afford it, and who haven't already performed it.
Eid ul Adha is an annual activity celebrated by all.
Festivals in Islam are based on the lunar calendar - which is around 11 days shorter than the solar calendar, which most people in the world use in their day-to-day life.
Being based on the lunar calendar means the dates of both Eids change each year, but Eid al-Adha is always a little over two months after Eid al-Fitr.
On both Eids, many Muslims will go to special prayers at their local mosque and have a day of celebrations with family and friends.