1.  Freedom of religion in Mauritania
Freedom of religion in Mauritania is limited by the Government. The constitution establishes the country as an Islamic republic and decrees that Islam is the religion of its citizens and the State. Non-Muslim resident expatriates and a few non-Muslim citizens practice their religion openly with certain limitation on proselytization and transmission of religious materials.
Relations between the Muslim community and the small non-Muslim community are generally amicable.
 

Religious demography
The country has a total area of 397,840 square miles (1,030,400 km²), and its population is approximately 2.5 million. Almost all of the population are practicing Sunni Muslims. There is a small number of non-Muslims. Roman Catholic and non-denominational Christian churches have been established in Nouakchott, Atar, Zouerate, Nouadhibou, and Rosso. A number of expatriates practiceJudaism but there are no synagogues. There are several foreign faith-based nongovernmental organizations (NGO's) active in humanitarian and developmental work in the country.

2.  Mauritania CIA Factbook
Religions:

Muslim (official) 100%
Population:

3,359,185 (July 2012 est.)
country comparison to the world: 133