In 1982, the United States of America once again found itself committed to a military intervention to restore peace in Lebanon. The latest eruption of violence began in June when Israeli Defense Forces launched Operation Peace of Galilee, invaded Lebanon, and besieged Beirut. In July, President Ronald Reagan committed U.S. Marines in a multinational force (MNF) of roughly 2,000 peacekeepers that also included French, Italian, and English forces. In stark contrast to the 1958 U.S. intervention, the MNF found itself in an ill-defined mission, caught in the middle of a conflict that entangled Palestinians, Israeli and Syrian armies, and warring Lebanese factions. This entry discusses the challenges and events that shaped the 1982 international military intervention in Lebanon.