The Islamic Resistance Movement, abbreviated Hamas (an acronym from the Arabic: حركة المقاومة الإسلامية, romanized: Ḥarakat al-Muqāwamah al-ʾIslāmiyyah), is a Sunni Islamist Palestinian nationalist political organisation with an armed military wing known as the al-Qassam Brigades. It has governed the Israeli-occupied Gaza Strip since 2007.

The Hamas movement was founded by Palestinian Islamic scholar Ahmed Yassin in 1987, after the outbreak of the First Intifada against the Israeli occupation. It emerged from his 1973 Mujama al-Islamiya Islamic charity affiliated with the Muslim Brotherhood. Initially, Hamas was discreetly supported by Israel, as a counter-balance to the secular Palestinian Liberation Organisation (PLO) to prevent the creation of an independent Palestinian state. In the 2006 Palestinian legislative election, Hamas secured a majority in the Palestinian Legislative Council by campaigning on promises of a corruption-free government and advocating for resistance as a means to liberate Palestine from Israeli occupation. In the 2007 Battle of Gaza, Hamas seized control of the Gaza Strip from rival Palestinian faction Fatah, and has since governed the territory separately from the Palestinian National Authority. After Hamas's takeover, Israel significantly intensified existing movement restrictions and imposed a complete blockade of the Gaza Strip. Egypt also began its blockade of Gaza at this time. This was followed by multiple wars with Israel, including those in 2008–09, 2012, 2014, 2021, and an ongoing one since 2023, which began with the October 7 attacks.

Hamas has promoted Palestinian nationalism in an Islamic context and initially sought a state in all of former Mandatory Palestine. It began acquiescing to 1967 borders in the agreements it signed with Fatah in 2005, 2006 and 2007. In 2017, Hamas released a new charter that supported a Palestinian state within the 1967 borders without recognizing Israel. Hamas's repeated offers of a truce (for a period of 10–100 years) based on the 1967 borders are seen by many as consistent with a two-state solution, while others state that Hamas retains the long-term objective of establishing one state in former Mandatory Palestine. While the 1988 Hamas charter was widely described as antisemitic, Hamas's 2017 charter removed the antisemitic language and declared Zionists, not Jews, the targets of their struggle. It has been debated whether the charter has reflected an actual change in policy.

In terms of foreign policy, Hamas has historically sought out relations with Egypt, Iran, Qatar, Saudi Arabia, Syria and Turkey; some of its relations have been impacted by the Arab Spring. Hamas and Israel have engaged in the protracted Gaza–Israel conflict, as part of the broader Israeli–Palestinian conflict. Hamas has attacked Israeli civilians, including through suicide bombings as well as launching rockets at Israeli cities. Australia, Canada, Ecuador, Israel, Japan, New Zealand, Paraguay, the United Kingdom, the United States, and the European Union have designated Hamas as a terrorist organization. In 2018 and 2023, motions at the United Nations to condemn Hamas failed to meet the two-thirds threshold.

Hamas is an acronym of the Arabic phrase حركة المقاومة الإسلامية or Ḥarakah al-Muqāwamah al-ʾIslāmiyyah, meaning "Islamic Resistance Movement". This acronym, HMS, was glossed in the 1988 Hamas Covenant by the Arabic word ḥamās (حماس) which itself means "zeal", "strength", or "bravery".

Hamas was established in 1987, and allegedly has its origins in Egypt's Muslim Brotherhood movement, which had been active in the Gaza Strip since the 1950s and gained influence through a network of mosques and various charitable and social organizations. Unlike other Palestinian factions, after the Israeli occupation of Gaza in 1967, the Brotherhood in Gaza refused to join the resistance boycott against Israel. In the 1980s, it emerged as a powerful political factor, challenging the influence of the PLO, whose Fatah faction it had played a core role in creating. In December 1987, the Brotherhood adopted a more nationalist and activist line under the name of Hamas. Hamas was initially discreetly supported by Israel as a counter-balance to the secular PLO. During the 1990s and early 2000s, the organization conducted numerous suicide bombings and other attacks against Israel.

In the Palestinian legislative election of January 2006, Hamas gained a large majority of seats in the Palestinian Parliament, defeating the ruling Fatah party. After the elections, conflicts arose between Hamas and Fatah, which they were unable to resolve. In June 2007, Hamas defeated Fatah in a series of violent clashes, and since that time Hamas has governed the Gaza portion of the Palestinian territories, while at the same time they were ousted from government positions in the West Bank. Israel and Egypt then imposed an economic blockade on Gaza and largely sealed their borders with the territory.

After acquiring control of Gaza, Hamas-affiliated and other militias launched rocket attacks upon Israel, which Hamas ceased in June 2008 following an Egyptian-brokered ceasefire. The ceasefire broke down late in 2008, with each side accusing the other of responsibility. In late December 2008, Israel attacked Gaza, withdrawing its forces in mid-January 2009. Since 2009, Hamas has faced multiple military confrontations with Israel, notably the 2012 and 2014 Gaza Wars, leading to substantial casualties. Hamas has maintained control over Gaza, often clashing with the Palestinian Authority led by Fatah. Efforts at reconciliation between Hamas and Fatah have seen limited success. Hamas continued to face international isolation and blockades, while engaging in sporadic rocket attacks and tunnel construction activities against Israel.