Ain al-Hilweh (variously, Ayn al-Hilweh, Ein al-Hilweh, etc.; the literal meaning is "sweet spring") (Arabic: عين الحلوة‎) is the largest Palestinian refugee camp in Lebanon with over 70,000 refugees, located on the outskirts of the port of Sidon. Because Lebanese Armed Forces are not allowed to enter the camp Ain al-Hilweh has been called a "zone of unlaw" by the Lebanese media. Many people wanted by the Lebanese government are believed to have taken refuge in the camp as a result of the lack of Lebanese authority.

The Palestinian cartoonist Naji al-Ali lived in Ain el-Hilweh in 1948 with his family after the Nakba during the 1948 Arab-Israeli war.

During the First Lebanon War (1982), the Israel Defense Forces (IDF) landed north of Sidon and the city was subjected to a heavy aerial bombing, causing heavy casualties among the civilian population. There was prolonged fighting in Ein el-Hilweh, culminating with the Palestinian defenders making a last stand at a mosque which was thereupon blown up by the IDF. Israeli historian Gil'ad Be'eri gives the following account