The Al Qasimi (Arabic: القاسمي, spelled sometimes as Al Qassimi or Al Qassemi; plural: Al Qawasem Arabic: القواسم and, archaically, Joasmee) is an Arab dynasty and tribe that rules Sharjah and Ras Al Khaimah, today forming two of the seven emirates of the United Arab Emirates. They are one of the longest reigning royal families in the Arabian peninsula. Historically, they also ruled over the town of Lengeh as sheikhs for a century until its annexation by Iran in 1887.

The Qawasem were a confederation of Sunni tribes in south eastern Gulf region surrounding the cities of Ras Al Khaimah and Sharjah; and faced strong rivalry with the Omani empire for naval domination along the Persian Gulf. Due to their allegiance to the Emirate of Dir'iyah, the British Empire branded them as "pirates" and fought two major military campaigns against them in 1809 and 1819.

The Qawasim tribe from which dynasty originates are Huwala, their ancestors migrating and keeping connections between the Arabian Peninsula and Persia, in particular maintaining their rulership over the town of Lengeh on the coast of Hormozgan province. The Qawasim tribe itself is of Hashemite origin, descending from Husayn ibn Ali, through their eponymous ancestor Al Qasim bin Idris bin Ja’far al-Zaki.

During the 18th century, the Arabian Peninsula witnessed a revolutionary socio-political and religious transformation under the reformers of the Muwahhidun (Unitarian) movement led by Muhammad ibn 'Abd al-Wahhab, often referred as Wahhabis. Embracing his ideals, the Qawasim robustly championed the doctrines of the Muwahhidun in the Gulf region and became a close ally of the Emirate of Diriyah.

By the early 19th century, the Qawasim emerged as a maritime power based both in Ras Al Khaimah on the Southern shore of the Persian Gulf and Qishm, Bandar Abbas and Lingeh on the Persian shore in the 19th century.

The Qawasim was a powerful naval force and sought to end the rising European colonial infiltration on their trade and commercial routes.

The British-allied Omani Empire had been the traditional enemy of the Qawasim over issues related to border disputes, religious differences and naval dominance in the Gulf. Qawasim control of trade in the Persian Gulf area led to wars with Oman and eventually with Oman's ally, Britain, and to the Qawasim (Joasmees to the British) being labelled by the British as pirates. This led to the identification of the southern shore of the Persian Gulf as the 'Pirate Coast', although following the General Maritime Treaty of 1820 and the 1853 Perpetual Maritime Peace, the various coastal emirates in the area became known as the Trucial States.

Beginning from 1804, there was a spike in Qawasim naval attacks on local trading ships. Following decades of incidents where native shipping had fallen foul of the aggressive Al Qasimi, a first British expeditionary force embarked for Ras Al Khaimah in 1809, the Persian Gulf campaign of 1809. This campaign led to the signing of a peace treaty between the British and Hussan Bin Rahmah, the Al Qasimi leader. This treaty broke down in 1815 and, in 1819, the British mounted a second, altogether more successful, punitive campaign against the Qawasim in Ras Al Khaimah under William Keir Grant.