An underground paramilitary Zionist group that operated in Palestine during the British Mandate period. (The name is Hebrew for “organization.”) It was established in 1931 by dissident Haganah members. The British considered it a terrorist organization; the dominant Labor Zionist movement considered it a radical rival, and in 1936, it became an instrument of the Revisionist Party, an extreme nationalist party. It was responsible for about 60 terror attacks targeting both British Mandate officials and Palestinian communities.

In 1941, the Irgun split into two groups: one became known as the Lehi or Stern Gang and regarded the British as the main enemy, and the other was closely allied to the Revisionist Party and regarded the Palestinians as the main enemy. The latter also organized illegal Jewish immigration into Palestine. Its members were executed by the British, and it in turn executed British army hostages. In 1946, the Irgun bombed the King David Hotel, which served as a British administrative command post, killing some 91 soldiers and civilians. Two years later, its members participated in the April 1948 massacre at the Palestinian village of Deir Yasin, just outside Jerusalem. By September 1948, the Irgun was dismantled and subsumed by the Israeli army. One of its leaders, Menachem Begin, later became prime minister of Israel. The Irgun was the precursor of the Herut Party, one of Israel’s most militant right-wing factions.