The group was founded during the first Intifada, and is considered a terrorist organisation by the European Union.
ADVERTISEMENTHamas, which has ruled the Gaza Strip since 2007, launched an attack inside Israel over the weekend, killing hundreds and taking others hostage. Its unprecedented breach of the border sent fighters inside border communities and military installations, shocked Israel and its allies, and raised questions about the group’s capabilities and strategy.
What is Hamas?
The group was founded in 1987 during the first intifada, or uprising, which was marked by widespread protests against Israel’s occupation.
The group has vowed to annihilate Israel and has been responsible for many suicide bombings and other deadly attacks on civilians and Israeli soldiers.
The EU and other Western countries consider Hamas a terrorist organisation.
Hamas won 2006 parliamentary elections elections and in 2007 violently seized control of the Gaza Strip from the internationally recognized Palestinian Authority. The Palestinian Authority, dominated by rival Fatah movement, administers semi-autonomous areas of the Israeli-occupied West Bank.
Israel responded to the Hamas takeover with a blockade on Gaza, restricting movement of people and goods in and out of the territory in a step it says is needed to keep the group from developing weapons. The blockade has ravaged Gaza's economy, and Palestinians accuse Israel of collective punishment.
Over the years, Hamas received backing from Arab countries, such as Qatar, as well as Turkey. Recently, it's moved closer to Iran and its allies.
Who are Hamas' leaders?
There were at least seven original founders of Hamas, including spiritual leader Sheikh Ahmed Yassin - a paralysed man who used a wheelchair - who spent years in Israeli prisons and oversaw the establishment of Hamas' military wing, which carried out its first suicide attack in 1993.
Israeli forces have targeted Hamas leaders throughout the years, and assassinated Yassin in March 2004. Another founder Abdel Aziz al-Rantisi was killed in Gaza in April 2004.
Khaled Mashaal, an exiled Hamas member who survived an earlier Israeli assassination attempt, became the group’s leader soon after.
Yehia Sinwar, in Gaza, and Ismail Haniyeh, who lives in exile, are Hamas' current leaders. They realigned the group’s leadership with Iran and its allies, including Lebanon's Hezbollah. Since then, many of the group’s leaders relocated to Beirut.
What does Hamas want?
Hamas has always espoused violence as a means to liberate occupied Palestinian territories and has called for the annihilation of Israel.
Hamas has carried out suicide bombings and over the years fired tens of thousands of increasingly powerful rockets from Gaza into Israel. It also established a network of tunnels running from Gaza to Egypt to smuggle in weapons, as well as attack tunnels burrowing into Israel.
In recent years, Hamas had appeared to be more focused on running Gaza than attacking Israel.
Why did Hamas launch an attack against Israel now?
In recent years, Israel has made peace deals with Arab countries without having to make concessions in its conflict with the Palestinians.
The US has also been trying to broker a deal between Israel and Saudi Arabia, a bitter rival of Hamas' Iranian backers.
Meanwhile, Israel's new far-right government was working to cement Israeli settlements in the West Bank despite Palestinian opposition and international condemnation.
Hamas leaders say an Israeli crackdown on militants in the West Bank, continued construction of settlements - which the international community considers to be illegal - thousands of prisoners in Israeli jails, and its ongoing blockade of Gaza pushed it to attack.
ADVERTISEMENTIts leaders say hundreds of its 40,000 fighters took part in the assault. Israel says the group has about 30,000 fighters and an arsenal of rockets, including some with a range of about 250 kilometres, and unmanned drones.