The Shammar are a tribal confederation made up of three main branches: the Abdah, the Aslam, and the Zoba. The modern tribe of Shammar are descendants of the Tayy tribe of Yemen. The earliest non-Arab sources refer to Arabs as Taits, thought of as referring to the Tayy, as Ayas ibn Quasiba, a ruler of pre-Islamic Iraq, had contact with both the Byzantine and Persian Empires. Sections of Tayy began migrating to neighboring regions such as Iraq and Syria before the existence of Islam. Tayy participated heavily in the Muslim conquests of the early centuries of Islam, with sections or individual members of the tribe settling in many parts of the Islamic Empire, including Lebanon, Palestine, Egypt, Libya, Tunisia, Algeria and Morocco. Most of these, however, were later assimilated into the local populations or into other tribes.
In the Namārah Inscription (the second oldest pre-Islamic Arabic inscription, dating from 328 CE), the name "Shammar" is believed to refer to a city in Yemen, though it may refer to the city where the Himyarite King Shammar Yahri'sh lived, the present-day Rada (located about 100 kilometres (62 mi) from Dhamar, an ancient historic site). Since King Shammar Yahri'sh ruled during the last decade of the 3rd century AD, it could be referring to the city he lived in or one named after him. It could also be referring to the city of Hayel, although there is no evidence that Imru Al-Qays fought the Tayy.
Led by Usma bin Luai the Tayy invaded the mountains of Ajaa and Salma from Banu Assad and Banu Tamim in northern Arabia in their exodus from Yemen in 115 CE. These mountains are now known as Jabal Shammar. The Tayy became nomadic camel-herders and horse-breeders in northern Nejd for centuries. Because of their strength and blood relations with the Yemenite dynasties that came to rule Syria (The Ghassanids) and Iraq (The Lakhmids), the Tayy expanded north into Iraq all the way to the capital at the time, al-Hirah. The area of the two mountains subsequently came to be known as "Jabal Shammar" ("Shammar's Mountain") from the 14th century, the first time that the Shammar as a tribe were noted in literature. In modern times, it is believed by some genealogists that the Tayy were absorbed into the Shammar tribe.