The Emirate of Trarza (arabic: إمارة ترارزة) was a pre-colonial state in what is today southwest Mauritania. It has survived as a traditional confederation of semi-nomadic people to the present day. Its name is shared with the modern Region of Trarza. The population, a mixture of Berber tribes, had been there for a long time before being conquered in the 11th century by Hassaniya Arabic speakers from the north.

Europeans later called these people Moors/Maures, and thus have titled this group "the Trarza Moors".

Trarza, founded in the midst of the final wars between the local Berber Bedouins and the Arab colonizers of the Maghreb, was organized as a semi-nomadic state led by a Muslim Prince, or Emir. Trarza was one of three powerful emirates that controlled the northwest bank of the Senegal River from the 17th to the 19th centuries CE; the others were the emirates of Brakna, and the Tagant.

The Arab conquests had resulted in a society divided according to ethnicity and caste. The "warrior" lineages or clans, the Hassane, supposed descendants of the Beni Hassan Arab conquerors (cf. Oulad Delim) maintained supremacy and comprised the aristocratic upper ranks. Below them were ranked the "scholarly" or "clerical" lineages, who preserved and taught Islam. These were called marabout (by the French) or zawiya tribes (cf. Oulad Tidrarine). The zawiya tribes were protected by Hassane overlords in exchange for their religious services and payment of the horma, a tributary tax of cattle or goods. While the zawiya were exploited in a sense, the relationship was often more or less symbiotic. Under both these groups, but still part of the Western Sahara society, were the znaga tribes, people who worked in lower caste occupations, such as fishermen (cf. Imraguen), as well as peripheral semi-tribal groups working in the same fields (among them the "professional" castes, mallemin and igawen). All these groups were considered to be among the bidan, or Arab whites.

Below them were ranked groups known as Haratin, a "black" population (ethnic sub-Saharan). They are generally considered descendants of freed slaves of sub-Saharan African origins; some sources suggest they were descendants of the first inhabitants of the Sahara. (Note that Haratin, a term of obscure origin, has a different meaning in the Berber regions of Morocco.) The Haratin often lived serving affiliated bidan (white) families; in this role, they were considered part of the bidan tribe, and not having tribes of their own.

Below them were enslaved persons. These were owned individually or in family groups. At most they could hope to be freed and rise to the status of Haratin. Rich bidan families generally held a few slaves for domestic use. Nomadic societies have less use of slave labor than do sedentary societies. In some cases, the bidan used slaves to work on oasis plantations: farming dates, digging wells, etc.

These interrelated tribes controlled distinct territories: the Emirates of Trarza, Brakna, and Tagant were the political reflection of Hassane-caste tribes in southern Mauritania. At the beginning of the 20th century, the French used tensions within this system to overthrow the rulers of Trarza and its neighbors and establish colonial administration.

In the 17th century, the French had established a trading post at the island Saint-Louis in the mouth of the Senegal River. The Bedouins of Mauritania came to control much of the trade from the interior that reached the French post. Trarza and other emirates profited from their raids against non-Muslims to their south by the seizure of slaves for sale and by the taxes they levied on Muslim states of the area. From the mid-18th to the 19th centuries, Trarza became involved deeply in the internal politics of the south bank of the Senegal. It raided and briefly conquered or backed political factions in the kingdoms of Cayor, Djolof, and Waalo.