In January 2006, Hamas gained control of the Palestinian Authority after participating in parliamentary elections for the first time and winning in 76 of 132 seats.
Hamas defeated the ruling Fatah Party after campaigning against corruption and highlighting its focus on social programs in towns and refugee camps where the group builds schools, hospitals and religious institutions.
The organization grew out of the Muslim Brotherhood and has two branches: a political wing and a militant wing that carries out attacks against Israel. Hamas is considered a terrorist organization by the United States, Israel and the European Union.
In Arabic, the world "hamas" means zeal but the name also stands for "Harakat al-Muqawama al-Islamiya," or Islamic Resistance Movement.
Hamas opposes the Oslo Peace Process, which allows for Palestinian self-rule in areas of the West Bank and the Gaza Strip in return for recognition of Israel's right to exist.
Hamas has instead said it considers it a religious duty to eliminate Israel. To that end, the organization's goal is total Israeli withdrawal from Palestinian territories. As a long-term goal, Hamas wishes to establish an Islamic state on lands initially decreed as Palestine, most of which have been within Israeli borders since Israel's creation in 1948.
Hamas' political arm is known for humanitarian efforts in the West Bank and Gaza Strip such as building hospitals, schools, orphanages, mosques, health care clinics, soup kitchens and sports leagues. The Palestinian Authority largely failed to provide such services when controlled by Fatah.
Before winning majority control in the Palestinian Authority, Hamas functioned as an opposition group to the Fatah Party. Since the death of Palestinian leader Yasser Arafat in November 2004, it has taken part in local elections and won seats in areas including Gaza, Qalqilya and Nablus.
The military arm, known as the Izzedine al-Qassam Brigades, carries out attacks on targets in the occupied territories and inside Israel. It is believed to have killed more than 500 people in more than 350 terrorist attacks since 1993 using mortars, short-range rockets, small fire arms and suicide bombers.
Following several deadly bus bombings in 1996 and 1997, the Palestinian Authority launched a clampdown on the organization, arresting about 1,000 Palestinians and taking over mosques in Gaza.
Israel assassinated Hamas' spiritual leader and founder Sheikh Ahmed Yassin in March 2004. After his death, Hamas chose hard-liner Abdel Aziz Rantisi as its leader in the Gaza Strip. Rantisi was assassinated in April 2004 leaving Khaled Mashaal as the group's leader.
Mashaal helped negotiate a truce in 2003 that temporarily stopped Palestinians attacks on Israel. In 1997, agents from Israel's Mossad poisoned him. He survived when Jordan's King Hussein coerced Israel into providing the antidote.
Hamas announced a truce with Israel in late 2005 as it prepared to run in the Palestinian elections for the first time, using Israel's withdraw from Gaza in August as part of its political campaign.
Shortly after Hamas' win and its refusal to change its hard-line policies, the United States and Europe cut funding to the Palestinian Authority.
The Palestinian Authority depends on outside aid to pay its workers and provide services to its residents. Some Muslim charities in the United States, Canada and Western Europe contribute money to Hamas for its social service groups.
Even after Iran pledged $50 million and other Muslim nations promised around $80 million, the funding cuts posed a financial crisis for the government. Hamas officials claim they need $115 million every month to pay Palestinian salaries.
Hamas chose Ismail Haniyeh as its prime minister and Khaled Mashaal as its political leader. While Haniyeh is considered a moderate willing to discuss peace with Israel, Mashaal adheres to Hamas' charter that calls for the destruction of Israel.
"Hamas will not recognize Israel. We will not give legitimacy to occupation," Mashaal told the BBC in February 2006.