The Banu Kalb (Arabic: بنو كلب, romanized: Banū Kalb) was an Arab tribe which mainly dwelt in the desert and steppe of northwestern Arabia and central Syria.

It was involved in the tribal politics of the Byzantine Empire's eastern frontiers, possibly as early as the 4th century. By the 6th century, the Kalb had largely adopted Christianity and came under the authority of the Ghassanids, leaders of the Byzantines' Arab allies. During the lifetime of the Islamic prophet Muhammad, a few of his close companions were Kalbites, most prominently Zayd ibn Haritha and Dihya, but the bulk of the tribe remained Christian at the time of Muhammad's death in 632. They began converting in large numbers when the Muslims made significant progress in the conquest of Byzantine Syria, in which the Kalb stayed neutral. As a massive nomadic tribe with considerable military experience, the Kalb was sought as a key ally by the Muslim state. The leading clans of the Kalb forged marital ties with the Umayyad family, and the tribe became the military foundation of the Syria-based Umayyad Caliphate (661–750) from the reign of Mu'awiya I (r. 661–680) to the early reign of Abd al-Malik (r. 685–705).

During the Second Muslim Civil War, the Kalb routed its main rival, the Qays, in the Battle of Marj Rahit in 684, inaugurating a long-running blood feud, in which the Qays eventually gained the advantage. In the resulting tribal factionalism which came to dominate Umayyad politics, the Kalb became a leading component of the Yaman faction against the Qays. The Kalb lost its political influence under the pro-Qaysite caliph Marwan II (r. 744–750), a situation which continued under the Iraq-based Abbasid Caliphate (750–1258). From its footholds in the Ghouta and Palmyra oases, the tribe revolted against the Abbasids on several occasions in the 8th–10th centuries, at first in support of Umayyad claimants to the caliphate and later as key troops of the Qarmatians, whose suppression contributed to the Kalb's political isolation. The Kalb remained among the three largest tribes of Syria at the start of Fatimid rule in the late 10th century, but due to its increasing sedentarism, it was disadvantaged to the more numerous and nomadic Tayy and Kilab tribes. The Kalb's relative weakness encouraged its close alliance with the Fatimids over the next century. This was occasionally interrupted, most notably when the Kalb joined the Tayy and Kilab in a rebellion to split Syria among themselves in 1024–1025, during which the Kalb failed to capture Damascus. The Kalb continued transitioning to a settled existence into the 12th century, after which the tribe no longer appears in the historical record.

Before Islam, the Kalb dominated the regions of al-Jawf and Wadi Sirhan, as well as the Samawa, the great desert expanse between Syria and Iraq. After the Muslim conquest, the tribe expanded its presence into Syria proper, taking the dominant position in the Golan Heights, the northern Jordan Valley, the Damascus area, and in and around Homs and Palmyra. As Fatimid rule progressed in the 11th century, the tribe's main concentration between Damascus and Palmyra shifted to the settled areas between Damascus, the Hauran, and the Anti-Lebanon Mountains.

The Kalb was a Bedouin (nomadic) tribe well known for raising camels. Before the advent of Islam in the 7th century, the tribe's grazing grounds were in northwestern Arabia. Its earliest known abode, during the Byzantine era (4th–7th centuries CE), was in the al-Jawf depression, including the oasis of Dumat al-Jandal. The tribe was mainly concentrated in this region, bordering the eastern frontiers of the Byzantine Empire. They seasonally migrated from there deep into the vast desert steppe between Syria and Mesopotamia, which the Arabic sources called the Samawa or Samawat Kalb, after the tribe, especially the southwestern part of this region. To the west of al-Jawf, the tribe's Banu Amir al-Akbar branch roamed between the oasis of Tayma in the south to the wells of Quraqir in the northern Wadi Sirhan depression. The Kalb began to expand its grazing territories eastward toward the Euphrates River, following the retreat of the Taghlib tribe in c. 570. The Kalb's tribal territory was bordered on the north by the powerful Tayy tribe, close allies of the Kalb. To the west, southeast, and east were the tribes of Balqayn, Ghatafan, and Anaza, respectively.

The Kalb's domination of Wadi Sirhan and al-Jawf put its tribesmen is a good position to migrate northward into Syria. With the advent of Islam in the 630s, the Kalb began to enter Syria in large numbers, at first making their abodes in the Golan Heights, the northern Jordan Valley, and in and around Damascus. Its tribesmen eventually became major landowners in the Ghouta gardens surrounding Damascus, as well as living a semi-nomadic existence in the Marj pasture grounds on the outskirts of the Ghouta. They also established themselves in and around Homs and Palmyra. A minor proportion of the tribe settled down in the garrison town and administrative center of Kufa in Iraq during the same period, while many Kalbite tribesmen established themselves in Muslim Spain as part of the Syrian expeditionary forces sent there in the 8th century.

At the time of the mid-10th-century geographer Ibn Hawqal, the diyar (tribal territories) of the Kalb extended from the area of Siffin near Raqqa, off the western bank of the Euphrates, to Tayma. This expanse excluded the area of al-Rahba and largely bordered the southern Syrian and northern Hejazi diyar of the Fazara tribe, a branch of the Ghatafan. Because of its inclination toward sedentarism, through the 10th century, the Kalb gradually lost its dominant position in the Dumat al-Jandal and Wadi Sirhan regions to its Tayy allies, while those who remained nomadic either migrated to join their kinsmen in central Syria or kept a low profile in their traditional dwelling places. Military pressures also forced the Kalb to retreat from the Homs area in the mid-10th century, its territory thereafter becoming restricted to the environs of Palmyra and Damascus.

Nomadic sections of the Kalb continued to inhabit the desert east of Palmyra into the late 11th century. After that point, even these nomadic groups shifted to sedentarism and the Kalb's main area of concentration shifted from the stretch between Damascus and Palmyra southwestward to the settled areas between Damascus, the Anti-Lebanon Mountains, and the Hauran, especially the last region. Smaller groups of the Kalb moved north of Homs and the Nile Delta in Lower Egypt around this time.