The Izz ad-Din al-Qassam Brigades (كتائب الشهيد عز الدين القسام; named after Izz ad-Din al-Qassam) is the military wing of Palestinian socio-political organisation Hamas. Created in 1992 under the direction of Yahya Ayyash, the primary objective of the group was to build a coherent military organization to support the goals of Hamas, which was at the time concerned with blocking the Oslo Accords negotiations. From 1994 to 2000, the Izz ad-Din al-Qassam Brigades carried out a number of attacks against both Israeli soldiers and civilians that endangered the peace process, ultimately giving way to the "Al-Aqsa Intifada", which Hamas enthusiastically supported.
At the beginning of the Second Intifada, the group became a central target of Israel. The group's strength and its ability to carry out complex and lethal attacks surprised many observers. The Izz ad-Din al-Qassam Brigades operated several cells in the West Bank, but most of them were destroyed by 2004 following numerous Israeli Defense Forces (IDF) operations in the region. In contrast, Hamas retained a forceful presence in the Gaza Strip, generally considered its stronghold.
The Izz ad-Din al-Qassam Brigades is listed as a terrorist organization by the European Union, the United States, Australia and the United Kingdom.