Lambert Adolphe Jacques Quetelet (22 February 1796 – 17 February 1874) was a Belgian astronomer, mathematician, statistician and sociologist. He founded and directed the Brussels Observatory and was influential in introducing statistical methods to the social sciences. His name is sometimes spelled with an accent as Quételet.

Adolphe was born in Ghent, Belgium, the son of François-Augustin-Jacques-Henri Quetelet, a Frenchman and Anne Françoise Vandervelde, a Belgian. His father François was born at Ham, in Picardy, and being of a somewhat adventurous spirit, crossed the English Channel and became a British citizen and the secretary of a Scottish nobleman. In this capacity he travelled with his employer on the Continent, particularly spending time in Italy. At aged about 31, he settled in Ghent and was employed by the city, where Adolphe was born the fifth of nine children, several of whom died in childhood.

Francois died when Adolphe was only seven years old. Adolphe studied at the Ghent lycée, where he started teaching mathematics in 1815 at the age of 19. In 1819 he moved to the Athenaeum in Brussels and in the same year he completed his dissertation (De quibusdam locis geometricis, necnon de curva focal – Of some new properties of the focal distance and some other curves).