The Mirdasid dynasty (Arabic: المرداسيون, romanized: al-Mirdāsiyyīn), also called the Banu Mirdas, was an Arab Shia Muslim dynasty which ruled an Aleppo-based emirate in northern Syria and the western Jazira (Upper Mesopotamia) more or less continuously from 1024 until 1080.

The Mirdasids were a family of the Bedouin (nomadic Arab) tribe of Banu Kilab. The Kilab's ancestral home was in central Arabia and its tribesmen first established themselves in northern Syria and the western Jazira (Upper Mesopotamia) in the years after the 630s–Muslim conquest. A second major wave of Kilabi tribesmen migrated to northern Syria from Arabia in the 9th century. The political vacuum and frequent revolts throughout the region during that period paved the way for the Kilab to strengthen their influence, becoming the predominant tribe in the region north of the Palmyrene steppe and west of the Euphrates River by the early to mid-10th century.

A third major wave of Kilabi migrants, principally from the Abu Bakr branch of the tribe from which the Mirdasids sprung, had invaded northern Syria in 932. This Kilabi migration was encouraged or directly supported by the Qarmatian movement, a radical millennarian Shi'a Isma'ili sect that had spread from southern Iraq in the second half of the 9th century. Around this time, the Bedouin tribes of Syria and Mesopotamia experienced marked population growth, which coincided with rising grain prices. This, according to historian Thierry Bianquis, made the tribes "susceptible to Qarmatian [sic] propaganda denouncing the wealth of the urban Sunni population". The Kilab and other branches of the Banu Amir, such as the Uqayl, Qushayr and Numayr, provided the bulk of the Qarmatians' military personnel. The Qarmatian campaigns "led to fundamental changes in the distribution and relative strengths of the bedouin tribes in the Syrian and Arabian deserts", and was the most important such realignment of the Arab tribes until the 18th century.

The dominance of the Kilab prevented Muhammad ibn Tughj al-Ikhshid (r. 935–946), the ruler of Egypt and southern Syria, from exercising power in northern Syria, which he had conquered in the late 930s. He allied with part of the tribe, appointing one of its chiefs, Ahmad ibn Sa'id, as governor of Aleppo in 939. In the months after, al-Ikhshid's forces were driven out of northern Syria by the Abbasids. Between 941 and 944, the political situation there was fluid and at one point, al-Ikhshid reoccupied the region. He appointed Ahmad ibn Sa'id as governor of Antioch and the latter's brother, Uthman, as governor of Aleppo. Their appointments aroused the jealousy of other Kilabi chiefs. Seeking to replace their kinsmen, they invited the Hamdanids of Mosul to invade Aleppo with their assistance. The 13th-century historian Ibn al-Adim asserts that the internal divisions among the Kilab enabled the Hamdanid Sayf al-Dawla to establish his emirate in Aleppo. Due to incessant Bedouin raids against his subjects, Sayf al-Dawla expelled most of the tribes of northern Syria to the Jazira, except for the Kilab, which was the only Bedouin tribe authorized to inhabit the area.

Throughout the 10th and 11th centuries, the Kilab "represented an organised military force with powerful cavalry trained in mounted swordsmanship and not fearing to confront a government army on the field of battle", according to Bianquis. Salibi notes that the northern Syrian Kilab's main military assets were its "Bedouin swiftness of movement" and its reservoir of tribal kin in the Jazira. The Kilab "served those who paid most and often, at a time of crisis, would sell their employer to the highest bidder", according to the historian Suhayl Zakkar. Kilabi tribes were involved in every Hamdanid struggle with the Byzantine Empire, which ruled the regions north of Syria, every uprising against the Hamdanids, and in intra-dynastic conflicts over the emirate of Aleppo. Between 1009 and 1012, the Kilab participated in the struggle for control of Aleppo between the emirate's ruler, Mansur ibn Lu'lu', and its former rulers, the Hamdanids, and their regional backers. Twice the Kilab betrayed the Hamdanids and their allies, and in return, demanded from Mansur numerous villages to supply them with grain, pastures to breed their flocks, and war horses. Instead, Mansur, who viewed the Kilab as a hindrance to his rule, strove to eliminate them by luring the tribesmen into a trap. To that end, in May 1012, he invited them to a feast, where his ghilmān (slave soldiers or pages; sing. ghulām) assaulted them. Several were killed and the rest were imprisoned in the citadel of Aleppo.

Among the Kilabi chiefs jailed by Mansur was Salih ibn Mirdas, the founder of the Mirdasid dynasty, whose family was based in the area of Qinnasrin. Salih had captured the fortress town of al-Rahba, situated along the Euphrates River, at the strategic crossroads between Iraq and Syria, in 1008, boosting his prestige among the Kilab and probably encouraging his wider territorial ambitions. Salih escaped imprisonment in 1014 and gained the allegiance of his tribesmen in Marj Dabiq, in the environs of Aleppo. Under his leadership, they defeated and captured Mansur, extricating major concessions in the subsequent negotiations to release him. These included the allotment of half of the Aleppo emirate's revenues to the Kilab and recognition of Salih as the paramount emir of the Kilab with formal authority over his tribesmen. In the following years, Salih consolidated his authority over the Kilab and expanded his emirate to include the important Euphrates fortress towns of Manbij and Balis.

The Egypt-based Fatimid Caliphate eventually gained authority over Aleppo, appointing Aziz al-Dawla as its governor there in 1017. Salih maintained friendly relations with him, while he strengthened his Jaziran emirate, which was centered in al-Rahba, where he formed an administration and presided over a tribal court. By 1022, he expanded this realm to include the twin Euphrates cities of Raqqa and al-Rafiqa. Aziz al-Dawla was killed that year and a period of chaos followed, but the Fatimids held onto the city. In 1023, Salih inaugurated an unprecedented military alliance of the Kilab and the two other strongest Arab tribes in Syria, the Banu Kalb of the Damascus region and the Jarrahid-led Banu Tayy of Transjordan, whereby the three tribes agreed to support the other in taking over Aleppo, Damascus, and Palestine, respectively, from the Fatimids. After backing the Tayy and Kalb in these efforts, Salih moved on Aleppo, capturing the town of Ma'arrat Misrin in its countryside from the Fatimids.

In late 1024, Salih's forces besieged Aleppo, capturing the city and its citadel from the Fatimids in early 1025, bringing "to success the plan which guided [Salih's Kilabi] forebears for a century", in the words of Bianquis. By then, he had also captured a string of central Syrian towns and fortresses, including Sidon on the Mediterranean, Baalbek and Homs, affording his new, Aleppo-based emirate an outlet to the sea and control of the trade route to Damascus. Despite his conflict with the Fatimids, he gave formal allegiance to the Fatimid caliph al-Zahir (r. 1021–1036), who, in turn, recognized him as emir of Aleppo. After Salih's Arab tribal alliance frayed with the defection of the Banu Kalb to the Fatimids in 1028, the Fatimid general Anushtakin al-Dizbari launched an assault against the Tayy in Palestine. Salih came to his ally's backing, but was slain in the Battle of al-Uqhuwana in 1029. This was soon after followed by the Fatimids resuming control over Salih's central Syrian domains.