Camps were set up across Lebanon after the 1948 Arab-Israeli war for Palestinians who fled their homes or were driven out by advancing Israeli troops.
Many of the refugees left with just the clothes the wore and a few possessions. Hundreds of villages were cleared and demolished.
The Palestinian presence in Lebanon's complex sectarian mix has continued to be a source of instability that has fuelled the conflict.
The worst incident was the Sabra and Shatila massacre by Lebanese Christian militias during Israel's occupation of West Beirut in 1982
The 1982 massacre shocked the world. Victims were buried in a mass grave a few hundred metres from Sabra and Shatila camps.
Sabra and Shatila were in the firing line again less than three years later, when the War of the Camps broke out in 1985.
Large numbers of Shatila residents fled the fighting between pro-Syrian forces and the Palestine Liberation Organisation.
Palestinian fighters in the camps were besieged as Syria and its allies tried to gain control of strongholds loyal to Yasser Arafat.
The War of the Camps went on for three years - one of the bloodiest and most destructive periods of Lebanon's long civil war.
The War of the Camps left Shatila in ruins. The original camp area was rebuilt, but refugees were prevented from reclaiming homes built in outlying areas.