Al Fadl (Arabic: آل فَضْل, ALA-LC: Āl Faḍl) were an Arab tribe that dominated the Syrian Desert and steppe during the Middle Ages, and whose modern-day descendants largely live in southern Syria and eastern Lebanon. The Al Fadl's progenitor, Fadl ibn Rabi'ah, was a descendant of the Banu Tayy through his ancestor, Mufarrij al-Jarrah. The tribe rose to prominence by assisting the Burids and Zengids against the Crusaders. The Ayyubids often appointed them to the office of Amir al-ʿarab, giving the Al Fadl emirs (princes or lords) command over the Bedouin tribes of northern Syria. Their function was often to serve as auxiliary troops.

Starting with Emir Isa ibn Muhanna, the Al Fadl became the hereditary holders of the office by order of the Mamluk sultans and were given substantial iqtaʿat (fiefs) in Salamiyah, Palmyra and other places in the steppe. By then their tribal territory spanned the region between Homs in the west and Qal'at Ja'bar to east, and between the Euphrates valley in the north to central Arabia in the south. Isa's sons and successors Muhanna and Fadl vacillated between the Mamluks and the latter's Mongol enemies, but generally they were highly favored by Sultan an-Nasir Muhammad. During late Mamluk rule, the tribe was occupied by internal strife.

The Ottomans preserved the Al Fadl's hereditary leadership of the Bedouin tribes. By the mid-16th century, the leading emirs joined the Mawali tribe and became known as Al Abu Risha, while their rivals within the tribe were driven out towards the Beqaa Valley and continued to go by the name "Al Fadl". The Mawali dominated northern Syria until the arrival of the Annazah tribesmen in the 18th century. During that same period, the Al Fadl in Beqaa split into the Hourrouk and Fa'our branches. The latter made its home in the Golan Heights where they often fought over pasture rights with Kurdish and Turkmen settlers, and later against Druze and Circassian newcomers.

Toward the end of the 19th century, the Al Fadl became semi-sedentarized; they settled in various Golan villages, but continued to shepherd their flocks, while their emir settled in Damascus and effectively became an absentee landlord who collected rent from his tribesmen. The Al Fadl were displaced from their homes in the Hula Valley and Golan during the 1948 and 1967 Arab-Israeli wars, respectively, and most settled in and around Damascus. As a result of the wars and Syrian agrarian reforms that stripped the emir of much of his land, his relationship with the tribe shifted from benevolent landlord to symbolic leader and political representative. By the 1990s, there were up to 30,000 Al Fadl tribesmen in Syria (not counting those who were affiliated with the Mawali) along with a significant population in eastern Lebanon.

The Al Fadl were one of the two main branches (the other being Al Mira) of the Banu Rabi'ah, a tribe belonging to the Banu Tayy (also known as the Tayyids). The Banu Rabi'ah were the offspring of the tribe's namesake, Rabi'ah ibn Hazim ibn Ali ibn Mufarrij ibn Daghfal ibn al-Jarrah. The Banu Rabi'ah were descendants of the 10th-century Jarrahid rulers of Palestine, and became prominent in Syria as a result of their participation in the Muslim war effort against the Crusaders, who conquered the Syrian (Levantine) coastal regions in 1099. The Banu Rabi'ah's branches Al Fadl and Al Mira (also spelled Al Murrah) were the descendants of Rabi'ah's sons, Fadl and Mira, respectively.

Fadl was noted in Muslim chronicles as an emir (prince) of the tribe by 1107. He and his brothers Mira, Thabit and Daghfal, and their father Rabi'ah, provided and commanded mounted auxiliary troops for Tughtekin (r. 1104-1128), the Burid ruler of Damascus, and his Zengid successors. By the time the Zengids gained control of the Syrian interior in the mid-12th century, the Banu Rabi'ah had become the dominant tribe in the Syrian Desert. Relations between the tribes and the various Muslim states were not always cooperative. During periods of strained relations the tribes would plunder the villages of the countryside and Hajj pilgrimage caravans.

The Tayyid roots of the tribe are supported and verified by Muslim historians. However, members of the Al Fadl have claimed fictitious lineages in the past, which have been dismissed by both medieval and modern historians. Among these legends was that the tribe descended from the Barmakids, a Persian household that held high office in the Abbasid government in Baghdad. That claim was disparaged by 14th-century Arab historian Ibn Khaldun. Some modern-era tribesmen have claimed descent from al-Abbas, the Abbasids' namesake and ancestor, and through him trace their lineage to the Quraysh tribe of the Islamic prophet Muhammad. In another story, descent is claimed from Abbasa, a sister of Abbasid caliph Harun al-Rashid.

At some point during Ayyubid rule in the late 12th century or early 13th century, the Al Fadl were driven out of Hauran in southern Syria by the Al Mira. They consequently migrated north to the steppe regions around Homs in northern Syria and were paid by the Ayyubid sultans of Egypt to ensure the safety of the roads connecting Syria with Iraq. The Al Fadl grew more powerful throughout this period due to the patronage of various Ayyubid rulers. Sultan al-Adil (r. 1200–1218) appointed Haditha, a grandson of Fadl ibn Rabi'ah, as amir al-ʿarab (commander of the Bedouin), an office denoting the chief of the Bedouin tribes that were under the jurisdiction of al-Adil and his Ayyubid kinsmen in the Damascus and Hama principalities. The jurisdiction of the amir al-ʿarab was later extended to the tribes around Aleppo by that principality's Ayyubid emir, az-Zahir Ghazi, during the latter half of his reign (1186–1218). Thus, the Bedouin tribes of northern Syria were put under the authority of Haditha; until then, the Banu Kilab had unofficially served as leaders of the northern Syrian tribes in place of their Mirdasid kinsmen.