Hamas (حماس Ḥamās, an acronym of حركة المقاومة الاسلامية Ḥarakat al-Muqāwamat al-Islāmiyyah, meaning "Islamic Resistance Movement") is a Palestinian Islamic socio-political organization which includes a paramilitary force, the Izz ad-Din al-Qassam Brigades.. On January 25, 2006, Hamas won the legislative elecions held in the Palestinian Territories, gaining the majority seats in the Palestinian parliament. This further complicated matters in the Israeli-Palestinian conflict as it is considered wholly, or in part, a terrorist organization by certain countries and supranational organizations. Since June 2007, after winning a large majority in the Palestinian Parliament and defeating rival Palestinian party Fatah in a series of violent clashes, Hamas has governed the Gaza portion of the Palestinian Territories.

Hamas was created in 1987 by Sheikh Ahmed Yassin, Abdel Aziz al-Rantissi and Mohammad Taha of the Palestinian wing of Egypt's Muslim Brotherhood at the beginning of the First Intifada, an uprising against Israeli rule in the Palestinian Territories. Hamas launched numerous suicide bombings against Israel, the first of them in April, 1993. Hamas ceased the attacks in 2005 and renounced them in April, 2006. Hamas has also been responsible for Israel-targeted rocket attacks, IED attacks, and shootings, but reduced those operations in 2005 and 2006. In 2008 the rockets reached their peak and then once again went down after Operation Cast Lead.

In January 2006, Hamas was successful in the Palestinian parliamentary elections, taking 76 of the 132 seats in the chamber, while the previous ruling Fatah party took 43. After Hamas's election victory, violent and non-violent infighting arose between Hamas and Fatah. Following the Battle of Gaza in June 2007, elected Hamas officials were ousted from their positions in the Palestinian National Authority government in the West Bank and replaced by rival Fatah members and independents. Hamas retained control of Gaza. On June 18, 2007, Palestinian President Mahmoud Abbas (Fatah) issued a decree outlawing the Hamas militia. Israel immediately thereafter imposed an economic blockade on Gaza, and Hamas repeatedly launched rocket attacks upon areas of Israel near its border with Gaza. After the end of a six-month ceasefire the conflict was escalated, and Israel invaded Hamas-ruled Gaza in late December, 2008. Israel withdrew its forces from Gaza in mid-January, 2009.