The Ezzedeen-al-Qassam brigades are the military wing of Palestinian resistance movement Hamas. Created during the 90’s under the direction of Yahya Ayyash (assassinated by Israel in 1996), the primary objective of the groups was to build a coherent military organisation fighting to reach the goals of Hamas. In the period going from 1994 to 2000, the Ezzedeen-al-Qassam brigades carried out a number of attacks against both Israeli soldiers and civilians that endangered the peace process following the Oslo Accords, which Hamas opposed.

At the beginning of the Al-Aqsa intifada, the group quickly raised as the number one enemy of Israel. The group strength and its ability to carry out complex and lethal attacks surprised many observers. The Ezzedeen-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. However, the situation is different in the Gaza Strip, the stronghold of the group, where the Ezzedeen-al-Qassam brigades continued to pose a major threat to soldiers and settlers. Until the February 2005 ceasefire between the Palestinian Authority and Israel, the group's strength in Gaza increased.

The fighters identities and positions in the group remain secret until their death: even when they fight against Israeli incursions, all the militants wear a characteristic black hood on which the group’s green headband is attached. The Ezzedeen-al-Qassam brigades operate from a model of independent cells and even high-ranking members are often unaware of the activities of other cells, which allows the group to consistently regenerate if some members are killed. During the Al-Aqsa intifada, the leaders of the groups where constantly targeted by the IDF during numerous airstrikes that killed many of them, including top leaders such as Salah Shahada and Adnan al-Ghoul. The current leader of the brigades, Mohammed Deif, remains at large and survived at least 5 assassination attempts.

In 2003 and 2004, The Ezzedeen-al-Qassam brigades in Gaza developed in a powerful organisation that was able to resist many IDF incursions, a situation which climaxed during the Jabalya siege of October 2004 (see Operation Days of Penitence). However, these battles took a heavy toll in the brigades ranks, with as many as several hundreds of its members killed. Surprisingly, the group seemed to keep gaining power and was able to carry out sophisticated attacks late in 2004 and in the beginning of 2005. The brigades can count on a huge pool of individuals seeking to join its ranks, on an important logistical organisation which supply the militants with weapons smuggled in Rafah using tunnels and on talented engineers who provide the fighters with homemade weapons such as the al-Bana, the Batar, the Yasin and the Qassam rocket.