Lake Chad (French lac Tchad) is a historically large, shallow, endorheic lake in Africa, the size of which has varied over the centuries. According to the Global Resource Information Database of the United Nations Environment Programme, it shrank as much as 95% from about 1963 to 1998, but "the 2007 (satellite) image shows significant improvement over previous years." Lake Chad is economically important, providing water to more than 30 million people living in the four countries surrounding it (Chad, Cameroon, Niger, and Nigeria) on the edge of the Sahara Desert . It is the largest lake in the Chad Basin.

Lake Chad is located mainly in the far west of Chad, bordering on northeastern Nigeria. The Chari River, fed by its tributary the Logone, provides over 90% of Lake Chad's water, with a small amount coming from the Yobe River in Nigeria/Niger. Despite high levels of evaporation, the lake is fresh water. Over half of the lake's area is taken up by its many small islands (including Bogomerom archipelago), reedbeds and mud banks, and a belt of swampland across the middle divides the northern and southern halves while the shorelines are largely composed of marshes.

Chad ⁱ/ˈtʃæd/ (French: Tchad, Arabic: تشاد‎ Tšād), officially known as the Republic of Chad, is a landlocked country in Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west. Due to its distance from the sea and its largely desert climate, the country is sometimes referred to as the "Dead Heart of Africa".

Chad is divided into multiple regions: a desert zone in the north, an arid Sahelian belt in the centre and a more fertile Sudanese savanna zone in the south. Lake Chad, after which the country is named, is the largest wetland in Chad and the second largest in Africa. Chad's highest peak is the Emi Koussi in the Sahara, and N'Djamena, (formerly Fort-Lamy), the capital, is the largest city. Chad is home to over 200 different ethnic and linguistic groups. Arabic and French are the official languages. Islam and Christianity are the most widely practiced religions.

Beginning in the 7th millennium BC, human populations moved into the Chadian basin in great numbers. By the end of the 1st millennium BC, a series of states and empires rose and fell in Chad's Sahelian strip, each focused on controlling the trans-Saharan trade routes that passed through the region. France conquered the territory by 1920 and incorporated it as part of French Equatorial Africa.